I would expect things like this from a game that was still in a beta, but that obviously isn't the case with ESO. These sorts of glitches, while not game-breaking, definitely ruin the immersion factor. See the screenshot below (link):
http://imgur.com/bfeOAGc
I've already finished all of the quests in Bal Foyen, and I just stopped back to do some resource collecting. The screenshot was taken at Fort Zeren (I chose to defend the docks instead of the fort during the Crossroads quest). In the foreground is Aera Earth-Turner, who is mourning over the corpses of Littrek and Denskar. In the background, standing around the cooking port, you see Littrek and Denskar again, very much alive. I can talk to them, and they repeat the same dialogue as from before the Crossroads quest. If I travel back to Dhalmora, Aera is there too, reciting even earlier dialogue. If I return to the beach where you first land after leaving Bleakrock, all of the NPCs are there - even the supposedly dead ones. I assume this is related to the phasing or layering technology not "updating" after quests are completed. It is as if all of the phases are active at the same time, so I get cloned NPCs, dialogue that doesn't fit, and basically a completely immersion-ruining experience.
Has anyone else experienced this?