Best I can do is to direct you to the Service-public website here: Généralités sur les demandes et remises de titres de séjour - Service-public.fr

Was looking for something else today when I noticed the little blue section at the top of the page. Apparently there is a big change going on for cartes de séjour for students and certain other categories. It's possible that your prefecture is simply waiting for the official word on how they are going to handle this, or that the promised interpretations just haven't yet been prepared and circulated.

All I can say is "welcome to France!" This kind of thing happens all the time, and no one at the prefecture will ever admit that they have no idea what is going on. Some changes in the law have been held up for YEARS awaiting publication in the Journal officiel of the details about the rules changes.
Cheers,
Bev