I’m on Old Blanchy (pve). My character has permanently had the pvp icon on my portrait for multiple days now, with pvp disabled the entire time, and it’s not just a visual bug because horde are able to attack me but I’m not able to attack them until they attack me. I also don’t get party buffs most of the time because most others are not flagged.
You probably have a PVP quest in your logs.
Check your quest log for “King of the Mountain” from Icecrown. It flags you pvp and will keep you flagged until you complete it or abandon it.