Spoiled? Why the Fels has the bar got spoiled food in the larder? Do they think if they're drunk enough they won't notice? Well... I hope they pay their latrine custodian well...
(Actually, can they can? Or I guess Merlin would say, tin?)
My guess is that it's some sort of moon rise curse. In the daytime it looks like a regular inn and you perceive it as a regular inn, including drink, food, and patrons. And then like... nighttime is zombie time.
If I had to guess what magics would go into a curse like that, I'd guess Change, Time, and incredibly powerful perception magic.