if I'm not wrong that isn't the user->id but the user->idnumber column (viewed as "ID number" in the profile page). Do you have information in that "ID number" field in order to be able to allow the process to effectively order by it?)

I've performed a quick look to code (not tested) and looks ok.

Ciao

Yes, I tested using that field too but the ordering in the auto-create preview didn't seem to take it into account. In fact I couldn't see any obvious logic as to how users had been sorted in to groups.