For me, finding a solution to this issue is No. 1 priority on the list of fixes and improvements to the game.
So, to recap, it could go something like this...
A colonist will not fire their weapon/will stop firing in the following circumstances:
a) At a hostile pawn if there is a chance of shooting a friendly colonist.
b) At a friendly pawn that has gone berserk.
c) At a prisoner who has gone berserk or is escaping.
In such circumstances, the pawn, if on automatic control, would select another available target to shoot at. If there were no other available targets, the pawn would hold its position and cease firing. The pawn's status would read as "Holding fire" to indicate that it would be shooting, but has stopped for one of the reasons listed above.
The human could make a conscious decision to shoot at the target by ordering a pawn to fire at the target, whether in automatic mode or manual mode.