Weapons disappearing when dropped into water, in trenches and in normal terrain

Weapons when dropped into water, be it by getting killed or be it dropping it deliberately makes them disappear. This is most prominently experienced in the river on Hue City. Sometimes it happens on Cu Chi as well. It weird why weapons should vanish in what is at max kneedeep water.

When being killed in trenches, be it Song Be, be it Hue City or be it Cu Chi, weapons vanish. Also enemy weapons vanish upon killing their holder.

It also happened to me in normal terrain or buildings. Killing an enemy and his weapon would vanish from the wooden floor. Or in some case he did not even drop his weapon at all.

Weapons disappearing when dropped into water, in trenches and in normal terrain