Sun Tzu and very annoying AI battlefield behavior

[tinkthank]

I have had this happen to me twice in a row:

- In a faraway province, I had assassins take out all Indy commanders, leaving nothing but chaff behind. My assassins moved on. So I sent in a flying unit (An Indy Caelum necromancer mage thingy costing 120 gold whose name I forget) to take the province, as I had no other troops around. It flies in, but I do *NOT* capture the province. Confused, I watch the replay. As is to be expected, the Indy province routs immediately (no commanders left), but the Caleum mage flies immediately to the extreme rear of the field and gets slaughtered by the routing infantrists.
Annoyed, I recruit another flying Caelum necromancer, but this time I set him to "cast spells" (before I did not set any battle orders).
But instead of casting "raise dead" (which he does normally until he is blue in the face, no matter what the circumstances), he again flies to the rear to insert himself between the routing enemies and the emergency exit, where he does absolutely nothing but bleed profusely.
Odd, don't you think?
Wouldnt it be wiser to have some commanders know when an enemy army is routing and avoid self-injury?

Sun Tzu says: Always leave the rear door *open* for your enemies to escape, so that they do not fight to the death.