Cata classic dungeon finder instances close when the instance is empty. Repeated times I have still been in the dungeon looting and then died, only to enter the dungeon to a new instance. I never received the items I won by roll but didn’t pick up before the instance closed.
I appreciate this is not quite a bug, but a resource management measure I suspect is a remnant of the past. It just feels cheap and quite out of place for a subscription game.