HI M.,
This might sound really strange, but chiropractic can help with this problem. I am a chiropractor (and have been for 14 yrs) and have seen a variety of potty training, including bedwetting, clear up after a few adjustments. For more info, go to www.icpa4kids.com (this is the website for the international chiropractic pediatric association, of which I am a member).
Also, since I do a lot of work with nutrition, sometimes, the pooping in the potty thing is related to decreased digestion of fats, proteins or carbs. That can also be ruled out as well, or ruled in. While it might seem that there is a psychological reason for this, it actually might be structural.
I'm happy to discuss this with you over the phone if you'd like. My office number is 215-345-WELL. Or, if you'd like to talk before then, email me and we'll setup a time. ____@____.com luck. N.