Explanation from D2 grognards wanted.

[Bowlingballhead]

Actually, it does sound like the 'no-retreat' clause went into effect, doesn't it? Long battle - 25 turns are taken up just killing the enemy's army. Turn 25 hits, and the sole remaining unit capable on Man's side (the militia) retreats. The iron dragons and clockwork horror cannot retreat, since they're mindless. Instead they shuffle around stupidly for another 25 turns, until the auto-death effect kicks in. The only thing that seems questionable is that there'd have to be some effect on the shambler king (slave collar, maybe?) that made him fearless.