Strange mushroom behaviour

[Reef Pilot]

This morning I noticed a couple of my fuzzy mushrooms puffed up in a ball inside out, with a small opening at the mouth. I have never seen this before. Normally they are just flat against a rock or sand. What are they doing?

By the time I grabbed a camera, the balloon shape was already subsiding, but you can still see the one on the right fairly blown up. 15 minutes later, they were normal.