@alpaca: I've reproduced it once, just to be sure it wasn't some temporary error. But I never checked if any other settlements were affected. In the files, antioch has:
- christianity 85 pagan 5 zoroastrian 10
I got christianity (=catholic) 85 zoroastrianism (=orthodox) 5 judaism 10.

Wait, I think I've discovered something. I changed the order in which the religions appear in the descr_beliefs. Zoroastrianism now comes 2nd, and Judaism 3rd. That means the engine perhaps can't handle them coming in the wrong order. I'll try something and will be back with more info.