Only tested in multiplayer. Not tested in single player.
When you spawn a wither and wait for it to "explode" and be fully active, if you attempt to fire and "new arrow" at it, the wither takes no damage and the effect that the arrow is supposed to apply, doesn't get applied.
PS WINDOWS 10 FOR LIFE!
Linked issues
Comments 2
The wither is supposed to be invincible before it explodes (though it's not supposed to attack either, are you getting MC-57569 also?)
same with ender dragon, most likely intended as they are boss mobs