This is still not correct fixed in 1.20. I don't exactly know what you changes though.
If a character (any actor in general) is to give you a weapon (Harris, Rowan, and Irale), one of two things should happen.
1) You don't have the weapon... so now you will receive the weapon and get the ammo associated with it (the exception is the Flamethrower Irale gives you.. which will give you 40 cells instead of 100.
2) You have the weapon, so the game should tell you "You Seem To Have Enough" and not receive the weapon and the associated ammo.
What Vavoom does is give you the weapon and its ammo, regardless of whether or not you already have said weapon.
I repeat... this only applies to the actors that give you said weapons.