Were you experiencing lag at the time? Sometimes the quest will complete and then try and complete again due to lag. You should have still gotten the items/sP from the quest and it should have taken the items.
Dexter by ❤
I just got on doing quests not controlling, I just create topic to inform about the issue, There was no lag anyway
Oh No! You aren't on a quest!
BUT, I know for a fact that I accidentally double-clicked on the turn-in quest button and got that... so maybe You are double-clicking?? Possibly?