I can also confirm this happening. If someone declines a dungeon while I am queued it is unlikely to pop for me afterwards. However a re-queue can get a instant pop. This occurs in queueing for dps/healer in all dungeons and raids.
Is this tied to queuing for multiple roles?
Also another bug that is similar is whereby the Activity Finder window for a dungeon is open upon arrival (in a dungeon). I believe this results from a group forming whilst you are zoning/being zoned.
Clicking either Accept or Decline on the Activity Finder whilst already in the dungeon will boot you, give you the deserter buff and leave your dungeon team one member short without the means to replace that member.
Letting the Activity Finder window time out might be a viable work around but i’m yet to test that.
Edit: Similar PVP occurrence without zoning on selecting role type and entering shambala. /Reloading the UI also results in ejection and deserter buff.