As Spy, changing your disguise weapon seems to be kinda hit or miss atm. It seems like some weapons of your disguise's loadout are okay to switch to, and the others just refuse to come up. The only instance I remember the specifics of was being able to pull up a Medic's crossbow and saw, but not the medigun. I've seen other posts regarding broken models for some weapons, like the Kritzkrieg. Related?