That happened to me but I just ignored it. Though I highly recommend you DO NOT scrap the room for that reason because morale doesn't do much anyway. And if every where else is happy then it doesn't really matter anyway.
I am having the exact problem with a mystery corpse, however, a person died in the room next to this one and not even in the same room. Their morale is down and they are complaining of working next to a corpse and yet no one in my vault is dead and there isn't a corpse in the room. Can this bug be fixed, please.
Oh, so THATS where I left the body! Alright, now I can bury this svcker and give Harry Potter back his invisibility cloak.
Thanks for the tip!
*Drags invisible body out feet first*