Undo suddenly stops working I have a file, that has A Mesh and an animated armature in it. Working with the mesh in Edit Mode is fine, Undo works. But as soon as I selected the Armature in any way, may it be in pose mode, edit mode or Object mode, Undo will stop working. Undo in Object Mode doesn't work for the Mesh too then.
Weightpainting like this is impossible..
When I go back into editmode of the Mesh it works again.

It seems like my Armature is interfering with the Undo-tools (all of them).
Is my Armature broken or what is it?

By the way I checked all the other common Undo-not-Working problems, My Keyboard-Layout doesn't change suddenly when working with the armature or something, its just weird.
It seems as checking Global Undo, in User Preferences --> Editing is solving that problem.