Otherwise some invalid pointers will be left which could be harmless if real object stays local, but crashes when linking them to another files. Was discovered here in the studio during Project Pampa, and the steps to reproduce are: - Create lib.blend, put armature and cube to it. Create a group with them. - Create scene.blend and link group from lib.blend. - Make a proxy from armature. - Make group real. - Add real objects to a group. - Create comp.blend and link group from scene.blend. This step will creah.