After placing down a Wither chest and removing it, the top part leaves behind an invisible block of which the outline can be seen, but cannot be interacted with. Attempting to interact with it in any way will behave as though there is still a block there. Maybe related to Issue #7?

Did this happen when you broke the top half r bottom half or happened for both?

Ok did a bit more testing. I should have mentioned that I was using the Mine spell from Electroblob's Wizardry... It only seems to happen when using that, whether you break the top or bottom half.

Fixed for v1.11