It happened to me once in Jade Forest, it was a moth, frog, snail combo if I remember correctly. Of course I needed all 3 at the time so was a pain to decide which one to pick.
"Even when you are winning soundly, you must always give your opponent a way to retreat with honor. If you don't, then he has no reason to surrender. He will fight until the bitter end, and you will pay a larger price for victory."