So this happened to me and my friends today.
We were looking for a party for Praetorium and the last healer kept withdrawing.
If this had happened once or twice, it could be a coincidence. However this happened over 20 times, all in quick succession. Ultimately, we had to change to a healer to get in on the first try.

Which made me wonder, shouldn't we have a 1-2 min wait to register again for duty if you've withdrawn from one? Cuz I think someone was having fun, registering and withdrawing from the dungeon ;P