So let’s say I have a potion in slot 1 on my bar. If I sign up to an Arena Skirmish using the pvp group finder, then rearrange my bar and move that potion to slot 2…when I get into the match it will revert to slot one. Then after the match, it is back in slot 2.
If I move the potion from slot 1 to slot 2 then sign up for arena finder, it doesn’t do that.
So it looks like being in queue, at least for pvp arena skirmishes, locks your bar until you requeue.