In Peaceful, when you try to create a wither, only the soulsand blockon wich you put the last witherskull and the skull remain.

The emplacement of the other blocks become glitchy, you "freeze" when you are inside.

Sames result when you try to re-create a wither using the remaing block.
But sometimes, only the central block remain and the skull became a squeleton skull instead of a wither-squeleton skull.