Do you have any baking pans or dishes that are stoneware and say microwave safe?
Well, they are, but they aren't.
If they have unglazed feet-or a section that is plain pottery- you could have problems with them cracking.
The reason is because water absorbs into the unglazed stoneware and when you put it in the microwave, the moisture heats up and pops and possibly causes cracks or breaking.
The best way to solve this problem is to make sure you don't soak the pan or dishes in water.
If it needs soaked, pour water into it.
Don't set the whole dish into the water.