I have the same issue. I do my share of 'crop dusting' with white smoke during regen when the conditions are right. It usually happens about 1minute after regen starts and I come to a stop long enough to let things cool down a bit. The moment I hit the gas, I'll belch white smoke for the next couple minutes. I think the ECM assumes the exhaust is hot enough to burn off all the extra fuel, but doesn't.

My dealer says this is perfectly normal. A friend of mine videoed his '10 belching smoke and crop dusting everyone behind him on the freeway and showed it to his dealer. They said it's normal also.