Issue was caused by performing conversion from FTFaces to materials from the end of lib_link_mesh, where tesselated faces were cleared already. This conversion can't be switched to BMesh structures because in future MTexPolys could be changed in a way, that versioning stuff wouldn't work any more. Another issue is that making such a conversion per-mesh would lead to quite a code spagetti, which is difficult to follow. Solved by splitting per-mesh cycle in lib_link_mesh, so now it consists of three steps: - Do linking stuff such as custom data layers, materials. Perform a Conversion stuff like tessface -> polys. - Convert all MTFaces to materials. This conversion handles all meshes and creates needed materials. - Free tessfaces, mark mesh as linked. Such a separation shouldn't noticeably affect on speed of linking.