I just did the rats quest and got no response when I got back to the inn, but I took two very small sidetracks (for goodies) after getting the quest and after killing the rats.
I added maybe 5-6 turns duration between accepting the quest and returning to the inn. So I figured it was either that, or the fact that I hadn't even researched Adventuring yet and the flavor text there implies I shouldn't have been able to enter the inn without it.