This is expected and has been covered a couple times before. Here is missy's explanation:
Originally Posted by
missydarlin
the reservations system and the airport system are separate.
[snip]
OLCI is attached to the airport system, so when you change seats through OLCI, its not going to display when you view your reservation online, but it will display if you go into OLCI again.
The seat you pick during OLCI will be the one you are assigned at the airport.