Two of my friends and I were running random dungeons tonight. We finished Spindleclutch I and then the random fourth person left the group so we re-queued for another random dungeon. The loading screen said it was Spindleclutch I again. When we ported in, we saw the blue portal you see when people are farther along in the dungeon and you need to catch up. We had a new fourth person in the group, not the previous random. He was nowhere in the dungeon and everything was dead. We realized that we'd been thrown back into the instance of Spindleclutch we'd just finished. So we decided to port to my house to try to queue for a new dungeon.

When we got there, the random we'd picked up for our fourth for this go was in my house. (If it matters, it's Sleek Creek in Rawl'kha.) We finally invited him to party chat and it turns out that he was a brand new player who had queued for his very first dungeon and instead of being put in the dungeon he ended up in some strange house and couldn't find anything to fight and didn't know what was going on. So we kind of adopted him for the evening and showed him around a bit. It was a nice encounter, to be honest. But it was the weirdest glitch I'd ever seen the dungeon finder make.

Throughout the evening as my friends dropped out, I'd get a notification that someone left our Spindleclutch I group and ask how I wanted to respond, and it said "in progress" on the upper right of my screen for the next two hours even though the dungeon was cleared and we weren't in it anymore.

TL;DR, upon queuing for a random dungeon as a group of three we were put in the same instance of the dungeon we'd just finished and our fourth player was put into my house.

It was funny and we made a friend out of it so I'm not complaining but I definitely wanted to report this as it was extremely unusual, just so it's on the record in case it points to some solution that helps with the ongoing long-term dungeon finder bugs. Or in case it starts happening to other people.