I've finished the Dawnguard quest a little while ago, and very shortly after this an Armored Troll appeared in Riften. It doesn't move or do anything and I can't talk to it and the guards and townfolks ignore it. It isn't in the way or anything or even that much of a bug, but I am a little worried that it may be an evolved Letrusch bug and in the end Riften will be buried under a mountain of trolls.

Anyone else experienced this, and is it a bug or actually intended?

hmm thats a new one for me perhaps try to kill it, then travel around some time, do some other quests etc, then return to see if it still respawns?