So...have been seeing this a few times now. Quest starting locations don't disappear when completing a quest after save/exit. Very easily reproducable.
- Get quest
- Save game and exit
- Reload game
- Complete quest
- Quest starting location is still there, but does nothing when you enter the tile. Quite annoying
Haven't done extensive testing, so can't say for sure if this applies to all quests or only certain ones....but I have seen it enough to think it warrants being reported 
Morten
