I had a similar event as well, except I never found the damned units.
Crushed most of the enemy, either dead or routed and out of the field of battle.
Game didn't end... spent the next 40 minutes combing the entire field looking for whatever unit the enemt still had. Ended up spreading my infantry units so thin that I had the entire field in full view at all times. No units anywhere.
"Close Defeat"