If it's active, this command will report your basic toggle settings: /melee
It does that "lock on target" thing and to stop you have to drop target. The plugin automates a lot of combat stuff so it's fairly useful. When manually playing, I try to pull with a ranged item/spell, if it locks on a target I mash ESC while backing up until it releases then book it back to camp.
If you want you can make a hotkey to temp disable it: /melee off
As a side note, I also notice this happens to me when I set myself as pullertank, and not just puller. The puller will start solo-meleeing the mob away from camp, which usually results in death or me fighting the stick on the mob manually.