Only poops while sleeping?

[lovebabies]

My DD is just 2, and is pt'd during waking hours, but I still put her in a diaper during naps and at nighttime. Somehow she only seems to poop during the times she's in a diaper. She does great on either her little toilet or the big one, so I don't think she's afraid to go there, but I want her to succeed at pooping on the potty (for my sake as well as hers ). Any ideas short of waking her up to get her to go? She had a couple of "accidental" successes while we were pt-ing, and she knows she gets a prize if she goes potty in the toilet, but she can't seem to make it happen. I'd love some advice!