Permanent Withers In The End

I spawned a wither in the End and while fighting it, the wither flew into a un-rendered chuck. I killed the original wither. However, now every time that specific chuck leaves my render distance and is then re-rendered, it re-renders with a new wither in it.

Please fix this bug. I have already killed had to face 15 withers, once with three at a time, and am getting quite annoyed as the withers are destroying everything on the main End island.