So, in a game I'm playing in we come up against one of these encounters. THe ones where we should not fight as we will lose. WE are about 6th/7th level and we are going up against a fiendish green dragon (total CR was 10 or so). The thing had a SR of 30, so none of the spellcasters had a chance of effecting it. I'm not sure how we were suppossed to get by it, but of course a fight breaks out. And due to some dumb luck we not only win, we lost no one. This is pretty amazing since most of the fighting was done by only one of our guys. Just one of theose wierd things.