I had the majority of my provinces Jewish (11 out of 19). The Jewish rebels then won and enforced their demands. I lost 50 prestige and had a big hit to LA in all the occupied provinces. But my religion was still Coptic. (I've actually bug reported the matter...)
There was a bug related to this. Fixing it now.
Jewish religion is actually in its own group (not pagan) but I used a bad template file when I did the results of enforcing demands.