I have checked DB entry info, and not all mobs of the same type are affected just a few, so some still appear correctly. Yet their DB data is exactly the same.
Also the grouping just modifies a players faction temporarily to the current party leader's faction and as this even happens to people that have never even been in a party it can't be that. And it also looks the same to everyone, Horde, Alliance, any player really.
And the auto-broadcaster just broadcasts server-wide messages, so that's totally unrelated.
It's not a GM mode bug as I've checked this on a non-gm account and a friend of mine also had the exact same issue on a non-gm account.