(v15, linux)
When one has a shotgun and ends turn while in active hands, the subsequent party members will have added fire mode button to their interface (I think only if they hold any firearm). The button does nothing for them if they don't hold a shotgun. It only influences the party members acting after such character (aka having lower initiative), the next round it's all anew.
I don't remember this seeing in v14, though could simply overlook.