Backpack dissapears when i unequip it. No matter if its full or not it just dissapears. I tried to look everywhere, switch to winter mode, but to no avail. I had the same bug with the pink kerfur (not omega), when I turned it on, sat on the quad bike and the kerfur just disappeared and was not displayed on the map.
I also came across a hook bug. I attached one end to a full barrel and the other to a quad bike, but the hook disappeared like in another bug. I don't have it in my inventory and it wasn't lying around anywhere, it just disappeared.