I've added the of_dynamic check and teleported around a few dozen maps in ToEE and KotB - didn't find any other cases. Back in Co8 7.4.0, most of the description box critters had it though. As for the Dolly issue - I think the reason was using daynight xfer with the same map for night and day. I haven't encountered other duplicates so far.
Dolly issue: this is due to duplicate mobs in the Hommlet Substitute map (from WotGS), which nevertheless have daynightxfers pulling them in from the other dimension over to map 5001. It's probably harmless, but I'll have to make sure...