Ah ha! This is exactly what was happening to me today in the pool. I couldn't understand why I was ok at the bottom, but kept floating to the surface when I started to swim. The instructor told me when some people kick, they just kick in a way that causes them to ascend. I didn't realize the significance of that until just now. I was swimming to the surface, not floating. That explains everything! Thanks!
I found this to be the most difficult part of the whole thing! And I admit, I bolted! More than once! LOL! But from the middle of the pool, so it wasn't that deep. I definitely don't want to be experiencing that panicky feeling 50' down. I had no trouble clearing the mask once I got it back on. That was easy, but breathing without it, hardest part of the whole thing I thought. Definitely need more practice there.