We assume this to be correct...
My active unit is attacked, and is in stalward, so I choose to counter attack. My opponents turn is over, so I continue to attack with the active unit that just happened to counter attack his unit. He is not Stalwart, thus he does not counter attack.
So, i get 2 attacks in a row for his one attack, even though he initiated it. Seems a bit odd. But does make some sense as I have more adjacent units, so I'm stronger. ? yeah ?