[Survival] Wither bug

Pyro: We had to learn it the hard way, right? Anyways, with the new survival, spawning the Wither allows it to grief, just as on SP (SinglePlayer). Back in old survival, this wasn't able to happen, and in the new survival, Creepers can't grief. If you could set the same for the Wither, it would be much appreciated.
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Map: I've had to make a place to spawn withers, as to not let our base get destroyed. ;-;