from the report... # bug 1. UV properties are not raw editable but are reported # as RAW_TYPE_INT by RNA causing wrong conversion # internally (bpy_rna.c line 2205) # bug 2. raw update of UV coordinates crash blender (rna_access.c line 252) mtfaces.foreach_set("uv", rawuvs) # workaround: #for i in range(int(len(faces)/4)): # mtfaces[i].uv = uvs[i] # bug 3. raw update of non-array property fails (rna_access.c line 2270) mfaces.foreach_set("material_index", mats) # workaround: # for i in range(int(len(mfaces))): # mfaces[i].material_index = mats[i] # bug 4. It is not possible to add a vertex color layer using mesh API. me.add_vertex_color() # no workaround...