I've got a mug that must have a crack or gap in the glaze, with the result that there's dampness is in the underlying bisque that gets very hot when I microwave a coffee back up to heat. In fact, the handle gets much hotter than the coffee, achieving the kind of temperature that would make the Joint European Torus proud.
I'd throw the mug away, but of course it's the one my daughter painted at a one of those creative cafe places, so it has sentimental value - even if she hates it.
Having just burnt my hand for the umpteenth time, WHY CAN I NEVER REMEMBER THE PROBLEM WITH THIS MUG?!!!!!!