diff --git a/source/blender/blenkernel/BKE_customdata.h b/source/blender/blenkernel/BKE_customdata.h
index e387fc5f97c..4736e7b7312 100644
--- a/source/blender/blenkernel/BKE_customdata.h
+++ b/source/blender/blenkernel/BKE_customdata.h
@@ -122,7 +122,10 @@ void CustomData_merge(const struct CustomData *source, struct CustomData *dest,
 void CustomData_bmesh_merge(struct CustomData *source, struct CustomData *dest, 
                             CustomDataMask mask, int alloctype, struct BMesh *bm, const char htype);
 
-/* frees data associated with a CustomData object (doesn't free the object
+/** NULL's all members and resets the typemap. */
+void CustomData_reset(struct CustomData *data);
+
+/** frees data associated with a CustomData object (doesn't free the object
  * itself, though)
  */
 void CustomData_free(struct CustomData *data, int totelem);
diff --git a/source/blender/blenkernel/intern/DerivedMesh.c b/source/blender/blenkernel/intern/DerivedMesh.c
index 1851042f84a..fd92b7b5d69 100644
--- a/source/blender/blenkernel/intern/DerivedMesh.c
+++ b/source/blender/blenkernel/intern/DerivedMesh.c
@@ -289,6 +289,13 @@ void DM_init(DerivedMesh *dm, DerivedMeshType type, int numVerts, int numEdges,
 	dm->needsFree = 1;
 	dm->auto_bump_scale = -1.0f;
 	dm->dirty = 0;
+
+	/* don't use CustomData_reset(...); because we dont want to touch customdata */
+	fill_vn_i(dm->vertData.typemap, CD_NUMTYPES, -1);
+	fill_vn_i(dm->edgeData.typemap, CD_NUMTYPES, -1);
+	fill_vn_i(dm->faceData.typemap, CD_NUMTYPES, -1);
+	fill_vn_i(dm->loopData.typemap, CD_NUMTYPES, -1);
+	fill_vn_i(dm->polyData.typemap, CD_NUMTYPES, -1);
 }
 
 void DM_from_template(DerivedMesh *dm, DerivedMesh *source, DerivedMeshType type,
@@ -466,11 +473,11 @@ void DM_to_mesh(DerivedMesh *dm, Mesh *me, Object *ob)
 	int totvert, totedge /*, totface */ /* UNUSED */, totloop, totpoly;
 	int did_shapekeys = 0;
 	
-	memset(&tmp.vdata, 0, sizeof(tmp.vdata));
-	memset(&tmp.edata, 0, sizeof(tmp.edata));
-	memset(&tmp.fdata, 0, sizeof(tmp.fdata));
-	memset(&tmp.ldata, 0, sizeof(tmp.ldata));
-	memset(&tmp.pdata, 0, sizeof(tmp.pdata));
+	CustomData_reset(&tmp.vdata);
+	CustomData_reset(&tmp.edata);
+	CustomData_reset(&tmp.fdata);
+	CustomData_reset(&tmp.ldata);
+	CustomData_reset(&tmp.pdata);
 
 	totvert = tmp.totvert = dm->getNumVerts(dm);
 	totedge = tmp.totedge = dm->getNumEdges(dm);
diff --git a/source/blender/blenkernel/intern/customdata.c b/source/blender/blenkernel/intern/customdata.c
index e1041391d3b..76ed8467c8f 100644
--- a/source/blender/blenkernel/intern/customdata.c
+++ b/source/blender/blenkernel/intern/customdata.c
@@ -1245,6 +1245,13 @@ void CustomData_update_typemap(CustomData *data)
 	}
 }
 
+static int customdata_typemap_is_valid(const CustomData *data)
+{
+	CustomData data_copy = *data;
+	CustomData_update_typemap(&data_copy);
+	return (memcmp(data->typemap, data_copy.typemap, sizeof(data->typemap)) == 0);
+}
+
 void CustomData_merge(const struct CustomData *source, struct CustomData *dest,
                       CustomDataMask mask, int alloctype, int totelem)
 {
@@ -1310,7 +1317,7 @@ void CustomData_merge(const struct CustomData *source, struct CustomData *dest,
 void CustomData_copy(const struct CustomData *source, struct CustomData *dest,
                      CustomDataMask mask, int alloctype, int totelem)
 {
-	memset(dest, 0, sizeof(*dest));
+	CustomData_reset(dest);
 
 	if (source->external)
 		dest->external = MEM_dupallocN(source->external);
@@ -1341,6 +1348,12 @@ static void CustomData_external_free(CustomData *data)
 	}
 }
 
+void CustomData_reset(CustomData *data)
+{
+	memset(data, 0, sizeof(*data));
+	fill_vn_i(data->typemap, CD_NUMTYPES, -1);
+}
+
 void CustomData_free(CustomData *data, int totelem)
 {
 	int i;
@@ -1352,8 +1365,7 @@ void CustomData_free(CustomData *data, int totelem)
 		MEM_freeN(data->layers);
 	
 	CustomData_external_free(data);
-	
-	memset(data, 0, sizeof(*data));
+	CustomData_reset(data);
 }
 
 static void customData_update_offsets(CustomData *data)
@@ -1372,9 +1384,10 @@ static void customData_update_offsets(CustomData *data)
 	CustomData_update_typemap(data);
 }
 
-int CustomData_get_layer_index(const CustomData *data, int type)
+/* to use when we're in the middle of modifying layers */
+static int CustomData_get_layer_index__notypemap(const CustomData *data, int type)
 {
-	int i; 
+	int i;
 
 	for (i = 0; i < data->totlayer; ++i)
 		if (data->layers[i].type == type)
@@ -1383,11 +1396,21 @@ int CustomData_get_layer_index(const CustomData *data, int type)
 	return -1;
 }
 
+/* -------------------------------------------------------------------- */
+/* index values to access the layers (offset from the layer start) */
+
+int CustomData_get_layer_index(const CustomData *data, int type)
+{
+	BLI_assert(customdata_typemap_is_valid(data));
+	return data->typemap[type];
+}
+
 int CustomData_get_layer_index_n(const struct CustomData *data, int type, int n)
 {
 	int i = CustomData_get_layer_index(data, type);
 
 	if (i != -1) {
+		BLI_assert(i + n < data->totlayer);
 		i = (data->layers[i + n].type == type) ? (i + n) : (-1);
 	}
 
@@ -1407,91 +1430,62 @@ int CustomData_get_named_layer_index(const CustomData *data, int type, const cha
 
 int CustomData_get_active_layer_index(const CustomData *data, int type)
 {
-	if (!data->totlayer)
-		return -1;
-
-	if (data->typemap[type] != -1) {
-		return data->typemap[type] + data->layers[data->typemap[type]].active;
-	}
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? layer_index + data->layers[layer_index].active: -1;
 }
 
 int CustomData_get_render_layer_index(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return i + data->layers[i].active_rnd;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? layer_index + data->layers[layer_index].active_rnd : -1;
 }
 
 int CustomData_get_clone_layer_index(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return i + data->layers[i].active_clone;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? layer_index + data->layers[layer_index].active_clone : -1;
 }
 
 int CustomData_get_stencil_layer_index(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return i + data->layers[i].active_mask;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? layer_index + data->layers[layer_index].active_mask : -1;
 }
 
+
+/* -------------------------------------------------------------------- */
+/* index values per layer type */
+
 int CustomData_get_active_layer(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return data->layers[i].active;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? data->layers[layer_index].active : -1;
 }
 
 int CustomData_get_render_layer(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return data->layers[i].active_rnd;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? data->layers[layer_index].active_rnd : -1;
 }
 
 int CustomData_get_clone_layer(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return data->layers[i].active_clone;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? data->layers[layer_index].active_clone : -1;
 }
 
 int CustomData_get_stencil_layer(const CustomData *data, int type)
 {
-	int i;
-
-	for (i = 0; i < data->totlayer; ++i)
-		if (data->layers[i].type == type)
-			return data->layers[i].active_mask;
-
-	return -1;
+	const int layer_index = data->typemap[type];
+	BLI_assert(customdata_typemap_is_valid(data));
+	return (layer_index != -1) ? data->layers[layer_index].active_mask : -1;
 }
 
 void CustomData_set_layer_active(CustomData *data, int type, int n)
@@ -1722,7 +1716,7 @@ int CustomData_free_layer(CustomData *data, int type, int totelem, int index)
 
 	/* if layer was last of type in array, set new active layer */
 	if ((index >= data->totlayer) || (data->layers[index].type != type)) {
-		i = CustomData_get_layer_index(data, type);
+		i = CustomData_get_layer_index__notypemap(data, type);
 		
 		if (i >= 0)
 			for (; i < data->totlayer && data->layers[i].type == type; i++) {
@@ -1737,7 +1731,6 @@ int CustomData_free_layer(CustomData *data, int type, int totelem, int index)
 		customData_resize(data, -CUSTOMDATA_GROW);
 
 	customData_update_offsets(data);
-	CustomData_update_typemap(data);
 
 	return 1;
 }
diff --git a/source/blender/blenkernel/intern/mesh.c b/source/blender/blenkernel/intern/mesh.c
index 449146fe640..c0a28c473f8 100644
--- a/source/blender/blenkernel/intern/mesh.c
+++ b/source/blender/blenkernel/intern/mesh.c
@@ -469,15 +469,17 @@ void free_dverts(MDeformVert *dvert, int totvert)
 
 static void mesh_tessface_clear_intern(Mesh *mesh, int free_customdata)
 {
-	if (free_customdata)
+	if (free_customdata) {
 		CustomData_free(&mesh->fdata, mesh->totface);
+	}
+	else {
+		CustomData_reset(&mesh->fdata);
+	}
 
 	mesh->mface = NULL;
 	mesh->mtface = NULL;
 	mesh->mcol = NULL;
 	mesh->totface = 0;
-
-	memset(&mesh->fdata, 0, sizeof(mesh->fdata));
 }
 
 Mesh *BKE_mesh_add(const char *name)
@@ -2125,8 +2127,6 @@ void BKE_mesh_convert_mfaces_to_mpolys_ex(ID *id, CustomData *fdata, CustomData
 	/* just in case some of these layers are filled in (can happen with python created meshes) */
 	CustomData_free(ldata, totloop_i);
 	CustomData_free(pdata, totpoly_i);
-	memset(ldata, 0, sizeof(*ldata));
-	memset(pdata, 0, sizeof(*pdata));
 
 	totpoly = totface_i;
 	mpoly = MEM_callocN(sizeof(MPoly) * totpoly, "mpoly converted");
@@ -2632,7 +2632,6 @@ int BKE_mesh_recalc_tessellation(CustomData *fdata,
 	}
 
 	CustomData_free(fdata, totface);
-	memset(fdata, 0, sizeof(CustomData));
 	totface = mface_index;
 
 
@@ -2777,7 +2776,6 @@ int BKE_mesh_mpoly_to_mface(struct CustomData *fdata, struct CustomData *ldata,
 	}
 
 	CustomData_free(fdata, totface);
-	memset(fdata, 0, sizeof(CustomData));
 
 	totface = k;
 
diff --git a/source/blender/blenkernel/intern/multires.c b/source/blender/blenkernel/intern/multires.c
index d34bb99ab98..66f2ff12258 100644
--- a/source/blender/blenkernel/intern/multires.c
+++ b/source/blender/blenkernel/intern/multires.c
@@ -2085,8 +2085,8 @@ void multires_load_old(Object *ob, Mesh *me)
 		CustomData_add_layer(&me->vdata, l->type, CD_REFERENCE, l->data, me->totvert);
 	for (i = 0, l = me->mr->fdata.layers; i < me->mr->fdata.totlayer; ++i, ++l)
 		CustomData_add_layer(&me->fdata, l->type, CD_REFERENCE, l->data, me->totface);
-	memset(&me->mr->vdata, 0, sizeof(CustomData));
-	memset(&me->mr->fdata, 0, sizeof(CustomData));
+	CustomData_reset(&me->mr->vdata);
+	CustomData_reset(&me->mr->fdata);
 
 	multires_load_old_vcols(me);
 	multires_load_old_face_flags(me);
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 02016b2597d..b49e392d1f4 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -3824,7 +3824,7 @@ static void direct_link_customdata(FileData *fd, CustomData *data, int count)
 	/* annoying workaround for bug [#31079] loading legacy files with
 	 * no polygons _but_ have stale customdata */
 	if (UNLIKELY(count == 0 && data->layers == NULL && data->totlayer != 0)) {
-		memset(data, 0, sizeof(*data));
+		CustomData_reset(data);
 		return;
 	}
 	
@@ -8098,6 +8098,7 @@ static void do_versions(FileData *fd, Library *lib, Main *main)
 		{
 			Mesh *me;
 			for (me = main->mesh.first; me; me = me->id.next) {
+				CustomData_update_typemap(&me->vdata);
 				CustomData_free_layers(&me->vdata, CD_MSTICKY, me->totvert);
 			}
 		}
diff --git a/source/blender/bmesh/intern/bmesh_mesh.c b/source/blender/bmesh/intern/bmesh_mesh.c
index 32879caec71..d3e3bcd3556 100644
--- a/source/blender/bmesh/intern/bmesh_mesh.c
+++ b/source/blender/bmesh/intern/bmesh_mesh.c
@@ -85,6 +85,11 @@ BMesh *BM_mesh_create(BMAllocTemplate *allocsize)
 	bm->stackdepth = 1;
 	bm->totflags = 1;
 
+	CustomData_reset(&bm->vdata);
+	CustomData_reset(&bm->edata);
+	CustomData_reset(&bm->ldata);
+	CustomData_reset(&bm->pdata);
+
 	return bm;
 }
 
diff --git a/source/blender/bmesh/intern/bmesh_mesh_conv.c b/source/blender/bmesh/intern/bmesh_mesh_conv.c
index b0a9168ffda..62abf43829b 100644
--- a/source/blender/bmesh/intern/bmesh_mesh_conv.c
+++ b/source/blender/bmesh/intern/bmesh_mesh_conv.c
@@ -536,7 +536,9 @@ void BM_mesh_bm_to_me(BMesh *bm, Mesh *me, int dotess)
 	oldverts = me->mvert;
 
 	/* don't free this yet */
-	CustomData_set_layer(&me->vdata, CD_MVERT, NULL);
+	if (oldverts) {
+		CustomData_set_layer(&me->vdata, CD_MVERT, NULL);
+	}
 
 	/* free custom data */
 	CustomData_free(&me->vdata, me->totvert);
diff --git a/source/blender/editors/mesh/mesh_data.c b/source/blender/editors/mesh/mesh_data.c
index a4640677a4e..5414ba2aefb 100644
--- a/source/blender/editors/mesh/mesh_data.c
+++ b/source/blender/editors/mesh/mesh_data.c
@@ -947,6 +947,7 @@ static void mesh_add_verts(Mesh *mesh, int len)
 
 	/* scan the input list and insert the new vertices */
 
+	/* set default flags */
 	mvert = &mesh->mvert[mesh->totvert];
 	for (i = 0; i < len; i++, mvert++)
 		mvert->flag |= SELECT;
diff --git a/source/blender/editors/mesh/meshtools.c b/source/blender/editors/mesh/meshtools.c
index 765f9307247..c0b6327d740 100644
--- a/source/blender/editors/mesh/meshtools.c
+++ b/source/blender/editors/mesh/meshtools.c
@@ -299,12 +299,12 @@ int join_mesh_exec(bContext *C, wmOperator *op)
 
 
 	/* setup new data for destination mesh */
-	memset(&vdata, 0, sizeof(vdata));
-	memset(&edata, 0, sizeof(edata));
-	memset(&fdata, 0, sizeof(fdata));
-	memset(&ldata, 0, sizeof(ldata));
-	memset(&pdata, 0, sizeof(pdata));
-	
+	CustomData_reset(&vdata);
+	CustomData_reset(&edata);
+	CustomData_reset(&fdata);
+	CustomData_reset(&ldata);
+	CustomData_reset(&pdata);
+
 	mvert = CustomData_add_layer(&vdata, CD_MVERT, CD_CALLOC, NULL, totvert);
 	medge = CustomData_add_layer(&edata, CD_MEDGE, CD_CALLOC, NULL, totedge);
 	mloop = CustomData_add_layer(&ldata, CD_MLOOP, CD_CALLOC, NULL, totloop);