Summary
When you summon a wither, and lead the wither into powder snow, the wither will destroy it. However, when it destroys the powder snow, it also drops the powder snow block. It is not supposed to happen.

Step to Reproduce
1. Summon a wither
2. Try to lead or push the wither to the powder snow to destroy it.
---> The powder snow block drops when the wither are inside powder snow.