When using a certain type of comb to a weapon (mostly seen on M4) and you have another full loaded comb kept in somewhere (backpack or t-shirt, whatever) suddenly without needing to press some button, appears an action message upon left corner of screen saying something like "Reload weapon" and pressing "F" it reloads with such kept comb, replacing current one equipped which disappears for good, couldn't find neither in backpack nor on floor.