I have had the same experience of the lower rate almost instantly disappearing off the 3rd. party website. Booked the lowest rate for the Chicago Indigo (it also luckly was refundable) only to have the claim disapproved because I had an approved claim within 30 days of the check-in. However the BRG telephone agent said other than that, it would have been approved. Mrs. Legal Eagle, whose shopping trip to Chicago it was to have been, then attempted the same reservation only to find the 3rd. party website had pulled its lower rate.
