Zakal, great point. While it would be good if all are creatures had logic and didn't attack a fire shield with only one health left, even if they already attacked it before, then that would be great. And if we could control creature logic even better.
But, I like your point that this is game mechanics better, and that by the logic we see of evey 1 attack or greater creature attcking when there's not a shield, that same creature would attack when there was a shield and therefore have the shield affect it.