Withers don't die in the void

Summary:
Withers will not die while in the void; instead, their death animation continues indefinitely producing some odd graphical effects.
Steps to Reproduce:
1. Dig out a 3x3 hole that leads directly to the void
2. Spawn or sumon a wither in the middle of the hole
3. Wait until the wither's health is drained from taking damage while in the void
Observed Results:
When the wither falls through to the void, it begins to slowly take damage. Eventually, when the wither's health is fully drained, it begins it's death animation; however, the death animation never ends and the wither never dies.
Expected Results:
The wither should die as it normally would, and carry out its death animation for a short amount of time.
Notes:
This bug does not occur when the wither is summoned in the void using the summon command; the wither must have time to charge and move on to its attack stage for the issue to occur.