I've also encountered a pretty annoying bug with undo after adding a new item/character:
1) open resources
2) select Animals_Rabbit_A (or anything else)
3) click on the "+" button at the top to add an item
4) click somewhere on the terrain
5) press ctrl-z to immediately undo adding the item
Result:
You get a pop-up dialog stating "The object is locked by source control!". After clicking the "OK" button, the object gets moved to the bottom left corner of the map, and cannot be deleted/edited anymore.
