When you queue up for anything, you wait until it has enough users to launch, and then click the 'join' or 'leave' buttons.
However as of late, for capture and hold PVP what actually happens is that when the queue has enough players to launch, it does so automatically, beams you up and drops in you the map.
THEN it gives you the 'join/leave' dialogue, which of course you can't select while on a queued map, and then the map goes "Hey, you're not supposed to be here" and kicks you out.
If you leave before it counts down (the queue join/leave) you can 'rejoin' via the queue menu, whereupon you'll get a 'joining in (0)' menu box. If you then start to log out the box will start counting down and if you're lucky you can log out and back in fast enough for it to actually put you in the bloody map.