pjz99 is right. Wrong grouping or incorrect joints are most probably reasons.

If you have "0" pose falloff zones shouldn't affect it. Does it apear when Michael has default pose? Can you hide it bending abdomen, thighs etc.? If yes, just adjust rigs in joint editor. Check either IK OFF.

If you created groups with Poser tool selecting incorrect polygon is very easy. Did you have message "Some polygons are outside selected groups" when you leaving setup room?
I recomend yopu create group before you open setup room. You can do it in another software. I usually use Wings, but instead of groups I create there material area (Wings does not create groups).
Anyway create groups first in posing room. Later (in posing room) create prop with each body part. Then carefuly check each prop (body part) hiding rest. Then you can notice for example that abdomen has additional polygon separated from the rest.

One more reason which can cause strange behaviour are thumbs with nudity in your library ;)