During the game, when I'm using the WIDOW MAKER, sooner or later, when I'm aiming it and try to shoot, the weapon won't fire. Then I have to go back to the menu and load a savegame to make it work properly again. I included a pic to give you more details on the weapon I am talking about.

yep, had the same bug, it not only applies to widow maker, it happens to all tech weapons where you can aim and charge.

I confirm that. I suffer it with my Nekomata sniper rifle.