When you are in a DZ and quit it or it kicks you out of the dz and puts you back in an OW zone if there is a pick of that OW zone it does not actually kick you from the zone and you are stuck in the DZ until you gate or the zone crashes you. For example. 54 people are in the DZ Fippy's revenge. If there are 20 people in OW Brells rest that has a limit of 60 people. only 40 people in the DZ will be kicked into OW and the remaining 14 people will be stuck in the DZ until they gate out because they would of been zoned out in the pick of OW brells rest. This is 100% reproduceable on all servers.
There's also the opposite of this problem, where you say "leave" or whatever to the NPC in an instance, and it boots you to a pick instead of the base zone. This results in half a group being in the base zone and the rest in a pick (or picks if there's more than one). Random and quite annoying.