It also happened to me and really pissed me off.
I was on standby and cleared. F was booked full but not all checked in yet. I was #1 on upgrade list. When I was about to board with my Y seat BP, I asked GA "Has F
boarded full"? "Yes" she replied without hesitation. I walked in and found a few open seats in F. What a lier.
What's worse, after a while I found on the website that I was cleared for F! Apparently somebody not showed up and the seat was given to me by computer. However, GA was too lazy to give me the new BP
