OK, lets see.....
FLAK Guns:
Flak Guns capable of firing AA & HE rounds will display the correct loadout.
Flak Guns not capable of AA (ack ack) will only display the HE loadout.
Deck Guns:
The deck gun will only EVER display HE rounds and the correct round count for that round.
Please note : All rounds displayed are clickable.
I can assure you that if you are seeing something different than this, somewhere along the line the 1024_768menu.ini has been changed from it's original state in GWX 2.1. I hate that file but I made sure it was correct before GWX 2.1's release.
List your activated mods if you like.