US Airways Dividend Miles (Pre-FlightFund Merger) - Upgrading US Flight Ticketed via UA codeshare

So, I wound up buying a PIT-PHL roundtrip through the UA website because the codeshares were cheaper than the same flights through the US website.

I called the Gold DM reservations line to apply an upgrade and get better seats. The agent told me that applying US upgrades on US flights ticketed through the UA codeshare could only be done "on the day of departure".

This sort of throws a wrench in the works for me. Should I expect this to change in the future, or is it a permanent situation? Not that upgrading the PIT-PHL segment is important to me, really, but it might be important to me on other flights in the future...

For the procedure for upgrading a US flight ticketed via the codeshare (using miles), also see the following thread:

http://www.flyertalk.com/forum/Forum51/HTML/004396.html

My recollection is that it was a mileage based upgrade only - but if they'll let us use the certificates, then that's a much better option.