that happened to me once. i called in and talked to the rep and they said that the backend system was acting weird. on a 764 it said i was like 30D or something like that even though i wanted row 16 or whatever it was and it kept switching me back. she checked the system and said on her side it showed up as the bulkhead row and to ignore what the website said and to just trust her and my seat is fine. when i checked in at the airport, it spat out a ticket for row 16 and all was well.

i would call in and check. if not, ask the person to go into their systems and change it for you so it sticks.