Something is definately wrong with the hero ai. They often just ignore flags completely. I often find Tahlkora right besides me, while her flag is set miles back. This is not an issue of a wrong ai setting. Even when set to "do not attack" I still often find my heroes at the front, when the flags tell them to be at the back. The only one who seems to be keeping his distance is Razah. But that's because he's set up as a minion master, so even without flags he automatically keeps his distance.