I'm saying it was done.
And yeah, I'm sure a lot of times the Germans may have been attempting a ruse.
Also consider that in a moment where a soldier thinks there's no way to survive except surrender, he may do so, only to begin to see ... "possibilities" as time goes on.
Somewhat aside from everything, there was a scene in the 1960 movie "The Longest Day" that provoked a great deal of controversy in its day. Just after much of the American soldiers managed to surmount the cliffs and begin to make progress, a few German soldiers come out of a bunker. One gets to say "Bitte Bitte" in the second or two before the American soldiers gun them down. As the American G.I.s leave, one remarks "I wonder what 'bitte bitte' means?" Well, what the German soldier was trying to say in English would be "please ---." We don't know what he was asking as of course he was so rudely cut off. Maybe it would be "Bitte, bitte, nicht shießen," which would be "please don't shoot." If this incident were true, would the American G.I. be considered guilty of a war crime?
Probably not, IMHO, as he was confronted by an enemy soldier in the heat of battle, obviously didn't understand the question or imploration the enemy soldier was making, and did what was expected of a soldier in a war at the time.
Yet it created a fireball of a controversy because "somehow" he was supposed to have "known" the German was trying to surrender.
There is also the true story of American soldiers at the Battle of the Bulge who were cut off and running out of ammo and tried to surrender to the Germans. One soldier who thought he knew a little German yelled "nicht shieß" (leaving off the last two letters "EN"). Unfortunatly this means, in German, "don't s**t." Apparantly even the Krauts didn't leave their sense of humor at home in WW2, so the krauts all broke out laughing, and accepted the surrender. It didn't do anyone of them any good because this was toward the end of the war.
I suspect things might have played out differently depending upon the scale too. A large scale matter involving officers might involve a great deal more formality than on a squad or platoon level.
But remember, in war, cr@p happens. It's nice to say there are rules of war, and of course there are. It would be nice if war itself was illegal and could be stamped out but that seems too "pie-in-the-sky" to ever happen. And just as it's impossible to preclude wars through the law, it probably will always be as hard to keep everyone playing by the rules -- especially when they interfer with survival.
The Roman Cicero said, "inter arma enim silent legges," meaning, "in war the law falls silent." When following rules makes you dead/defeated, there's an enormous almost insurmountable ambition to violate them for ones' own good, or that of the country you're serving.
That's why it's war, not pinochle.