Custom weapons have no sound when editing in G.E.C.K.

[guywithpie]

For some reason whenever I try to edit a weapon from a mod to make it more powerful, it loses its firing and equip sounds. If I make the weapon, close the G.E.C.K., then go back in all of the assigned sounds for the 2d, 3d, etc. sounds on the Art & Sound tab of the G.E.C.K. are empty, even if I didn't change them from the original sound of the weapon mod. I can edit custom weapons just fine so long as they have vanilla sounds, but for some reason custom sounds do not work. Am I doing something wrong? Any help would be appreciated.