Solved mcMMO is preventing PvP for certain players

Recently mcMMO started preventing PvP for three players on my server: me, a staff member, and a donator. I haven't added any special permissions to these groups. Unloading mcMMO fixes this problem, so I know for a fact it's mcMMO causing this.

mcMMO is a staple of my server, mainly for the repair, mining, and smelting skills, so simply uninstalling it isn't really an option. :/

Solved. We were all in a party. xD

EDIT by Moderator: merged posts, please use the edit button instead of double posting.