That does sound odd to me. None of my beardies have ever pooped in their sleep. How old and how big is Little Foot? I would try to get him to go during the day, so he's more likely to be empty when he goes to sleep. They usually go if you put them in a slightly warm bath. Depending on how big he is, you can put him in either the sink or a small bin with lukewarm water up to his elbows, and make sure you supervise him.

Hope that helps