if you could send me the save (email@example.com) I will try to repro it here and get that fixed... I've been told about this happening before but have never been able to get it to happen
1) Champion + regular units in the army
2) Fight a battle, let champion die during combat but let the regular units survive and win the battle.
3) Whole army is teleported back to nearest city, plus champion incurs an injury and doesn't gain XP.