In the mission, just wait a few seconds for the Opfor unit nearby to go into crouch stance, and then hit him in the leg, or hit nearby him, or run out into his view - as long as you are more than 20 meters out - any of these actions will reveal the issue, as the unit will just sit there and stare at the player, and will not target (lift weapon) nor fire. I have tested this out to 150 meters with the same results. The only time I have gotten the unit to fire is when I came within 10 meters of him, where he stands up and then fires.
If attempting to re-produce the issue in ones own mission, just set a lone enemy units init code to: This setBehaviour "SAFE"; This setUnitPos "MIDDLE"; And then set the player unit 50 meters away, and be sure initially that the enemy unit is not facing the player, so that when the test is started the enemy unit does not know about the player. Then from there, do the same as what the description at the top says for the provided test mission.