Yesterday I was queued for a normal random dungeon, and after about 10-15 mins of waiting, the group popped up. But a split second before I could even accept the teleport the game offers, someone left the group suddenly and it told me I cannot be teleported. Then I checked the dungeon finder tab screen and it informed me I had a 15 minute penalty before I could attempt to join again. Is this a bug? Can someone explain what happened? I know it's nothing I did because i literally touched or pressed nothing, the whole thing happened fast.
So I ended up having to wait for an additional 15 minutes before I could even wait for a new dungeon group.
Some guy on zone said it happens sometimes, but didn't know why.