I guess the problem with unbuttoning gunners is as follows: their quick unbuttoning doesn't match the behaviour of all other units in the game.
I'll explain myself:
You have an infantry platoon which has clear LOS on an enemy MG team (for example). The enemies haven't seen them yet, and you send your platoon on a frontal assault. As soon as they begin running, the MG would kill them in no time, so a realistic behaviour would have the leader of the platoon calling you SOB or something and refusing to acomplish that order. He's not going to commit suicide in such a ridicule way.
Nevertheless, ingame your pixel troops will begin the assault. After a few shots they will probably begin running for cover, but they DO charge the MG position.
In my opinion, gunners should work the same way. Even in a situation when common sense advises you to leave the gun unmanned and hide in the relative safety of your armor (call SOB your leader xD) , the pixel soldier should keep firing until you give him the order to button up, at least while he still has a high or average morale.
If the gunner of a Humvee hides after the first shots, then the platoon should refuse to even stand up in front of that MG.
Well, i have some problems with the language, but i hope i made myself clear