As you can see on the picture, it's now possible to place paintings on top of each other. I don't know when the bug came, since it's some time since I decorated with paintings..
Very easy to reproduce, just place some paintings on top of each other.
If you are in survival, you see that the amount of paintings you hold decrease as you place them, even though you can't see the one you place.
EDIT: Not that easy to reproduce.. it happends randomly