Yes I have found the same thing. Now they have a $29 fee to select "premium seats" at t24 and only a GA or in some cases other agents at the airport can move to the premium seats without collecting the $29 fee.

As a Diamond I can select the premium seats (all Plats and Diamonds can) at booking for my ticket but not companion when the companions ticket was not on the same reservation. I've spoken to several agents on the phone and they said they cannot change my companions seat to one of the $29 ones unless I paid to do so. Even when I said that they would be sitting in my seat in F and I would be in the Y seat it didn't matter.