Sorry to post without a solution, but I have had the same problem with my iPad (1st Gen) - since mid-May in fact. I've tried checking/unchecking (all photos, faces, events, etc), and they don't go away.
However I noticed the following. If you do check the faces you don't want, sync, and then look on your iPad/iPhone, all of the photos of those people will be there. However, if you then uncheck the faces you don't want, sync, and look at the iPad/iPhone again, you might notice that only a fraction of the photos for those people are "stuck" in the device. There's some kind of cutoff or threshold with this glitch.