What I expected to happen was...:
I was trying to spice up my map room (I have houses with maps in them and I managed to make my maps only show one house, each with a mp in it...) with the Wither Spawn painting added in 1.4.2

What actually happened was...:
Every other painting happened, and I checked the list, accept the Wither Spawn, and I tried for a good ten minutes

Steps to Reproduce:
1. GET PAINTING
2. TRY AND SPAWN IT
3. ...