I disagree, Super Market; sometimes you really want that fleeing unit to stay dead (e.g. when it's an enemy FM, or other elite).

As for your problem, Zing, I'm not sure. I recall a similar annoying problem occurring far too frequently in M2; cavalry ordered after fleeing enemies (either attacking or overrunning) would seldom seem to switch to couched lances, in fact, almost always preferred to use swords, even when charging at full tilt towards a stationary target. Worse, they would charge with lances ready, only to stutter and grab for their swords just moments before what would have been impact. ANNOYING!

...but that's not much help. Sorry :(