Anyone else having trouble with the "Raid the Bar" credit working properly?

I just left the Muse in NY on a great stay (they were wonderful). Gave the "Raid the Bar" card at checkout. I told them I took two bags of nuts at $6 each. They said not to worry about it because the $15 credit more than covers it... Yet I still had a $6.53 charge hit my credit card. How hard is it to properly execute this perk?