I was booking by the seat of my pants Friday and decided to run down to San Francisco for a weekend stay. I booked the reward at approximately 11am and checked into the hotel around 4:30pm. The weekend was ok (horrible weather) but this morning when I signed into my Marriott account to set up a biz trip i noticed I had been charged for an extra reward night. I called up the Platinum desk and talked with an extremely helpful gentleman who informed me that this sort of thing happens sometimes. My morbid curiosity got the better of me and we got to talking about the reason. Not surprisingly the system that generates the reward cert is different than the Res system and the two require some time to sync up. In my case, I checked into the hotel before the Cert system had generated and delivered the Cert despite the fact that the Res was set up as a reward stay. When the Desk checked me in, the Res system was unable to claim the cert and therefore requested a one night cert be generated to fulfill the requirement. This created the extra reward redemption. In the end the Plat Desk called the hotel and straightened things out and let me know my account would be credited within 72 hours. Just thought it was an interesting hiccup and something other frequent in-the-moment reward bookers should keep an eye on.