Ooh Marriott, you have been a naughty boy...

Apparently, if the first time Marriott run your card for a reservation and the Marriott system doesn't like what it gets back then they cancel your rate but if it goes through fine the 2nd time they run it then the system auto-rebooks you but at the rate at the time, which is likely to be noticeably higher.

There is clearly a flaw in Marriott's system, because they shouldn't cancel the original rate at the time of booking until all tries -- however many Marriott do -- are exhausted.

It seems like an easy enough fix for them to implement, they just have to have the system remember the original rate or not cancel it right away. And unless you cross-check your folio with the email made for the booking, you will not know.

And there are no obvious signs at the time either: Amex didn't contact me to say there was a problem and neither did the hotel when I checked in.

Not cool Marriott, not cool...