I understand in the new snapshots, clicking on an item frame to destroy it is actually supposed to drop the item, if there is one. The same happens if TNT explodes right next to it. I doubt this is intended. I would imagine that TNT should destroy the item frame no matter what, but if there is an item in the frame, the frame stays and the item pops out. If there is no item in the frame, the frame will drop like normal.