9151095dbe
Basically, issue is that outliner stores editbones for an edited armature, which are only valid during EditMode. When more than one object use the same armature, selecting ebones from same armature but under non-edited object would first select that object (and hence switch out of editmode), and then try to select editbone while editdata no more exist. Solution for now is to not change active object in this case - it's not totally ideal (not consistent), but other solutions (like switching edited object without leaving editmode, or rebuilding (part of) outliner tree in-between) are horribly hackish and most likely prone to epic failure anyway.