I had the same problem. I was in Glowecestrescire with a Theign cloak on. I speed traveled "home" nothing changed. But when I uncloaked in Glowecestrescire you could see the Mari Lwyd fur. From then on it stuck.
Could talk to Reda about the Haytham Quest but not about anything else
Same for me. And the corpse is still there but the key symbol is now gone, after 20 hours.