I have had several tests to try and figure it out.
Is the items that disapear isolated to resently picked up items?
-This does not seem to be the case, as i've lost "fresh" and "old" items.
Is the cause from swapping without dropping your current backpack?
-seems unrelated, as having it on or dropping the old one will yeild the same results.
Any way for this not to happen?
-Not realy, but if i drop everything on the ground. Change backpack/west and pick everything up, that seems to be close to a 100% sucsess.
-Dropping clothing on the ground seems to work. But i've had items disapear from the clothing thats unequped down on the ground.