I found the same problem when I recently bought a AC ticket in BKK (same CTO as UA, just different counters).

Jan 3 '03 YYC-YVR L fare (similar to V-W on UA) The agent couldn't book me in the more forward sections of the aircraft. She tilted her screen for me to see the seat map. Starting from the second row of economy, the window and isle seats were blocked to elites and higher (not middle seats, as already indicated). Even though I am 1P on UA, she was unable to assign me any of the blocked seats.

So, I settled for the first row behind 1st. I guess these are less desirable as the 1st class seats lean back, but at least I'm not way back there.

I wish they could fix that. No biggie.