Dragging items from the universal waist pack to the load-bearing vest doesn't work, though it does work the other way around—from the vest to the waist pack. You have to move the item out into the open first.
Reproduction steps
Dragging items from the universal waist pack to the load-bearing vest doesn't work, though it does work the other way around—from the vest to the waist pack. You have to move the item out into the open first.