Guns disappearing from save file

I have tried to find out why this keeps happening but no luck.

I made about a dozen or so custom weapons, all 'legit' according to GearCalc and they work fine in-game. The problem is that sometimes they will vanish from the save file. Usually the problem is the other way around, ie custom weapons are visible in the save file but not in-game.

Currently in have 24 usable weapons in-game but when I open the save with WillowTree or Gibbed's editor it only shows 20. 2 of those 4 'missing' weapons are in slots 1+2 in the game. I tried removing them but they are still invisible in the save editor.

It's not a big deal but I was just curious how the game could be showing and using weapons that can't be 'seen' by save editors?