When trying to aim using M4 red dot sight while in prone you get a black screen as if camera is inside some texture/model or something obsuring the view. The character had a gasmask, hunting backpack, army helmet and a black vest (not UK vest). M4 was with CQB stock and bipod installed.
The issue appears only in prone stance. Unable to reproduce due to character death and loss of all gear.

! Edit: Apparently the same as - http://feedback.dayzgame.com/view.php?id=4283