I don't remember ever getting this after Shadows Over The Sun...

[Nyx0tron]

 

[PalletTown]

It's a bug. It's suspected that it has something to do with the Titan's grip perk. It will also delete one of you equipped items, and hilariously enough, if you are unarmed, it will dupe the rusty knife.

 

[Gabranth]

Yeah, apparently that happened before TG was added, but it was rare.

Now it's a 100% thing in my experience.

 

[valk42]

enjoy your hilariously op weapon, friend