If you fire too fast with the combat shotgun during the shooting range, you will get the c-bug, regardless of whether you are standing or crouching.
I noticed that and wanted to report it now, but it seems that it also happens during normal use.
does the "anti-c-bug-system" work if the rate of fire is too fast? with automatic weapons like mp or something like that, that doesn't happen. maybe put the combat shotgung in the MP's drawer so that the system no longer works for combat shotgun