The only things that I know of that would make a unit uneligible for undisordering is being in covered terrain such as woods, marsh, town hexes, or being stacked with a unit of different formation (such as infantry in line with infantry in column, infantry with cavalry).
In other words, a unit doesn't undisorder under conditions where it would disorder. Sounds logical enough, come to think about it, doesn't it? [;)]
<center>Général de Division D.S. "Green Horse" Walter
Baron d'Empire, Duc des Pyramides
Commandant de la [url="http://home.arcor.de/dierk_Walter/NWC/3_VI_AdR_Home.htm"]3ème Division[/url], VIème Corps Bavarois, L'Armée du Rhin
Commandant l'Ecole de Mars, L'Armée du Rhin
Commandant de la Brigade de Tirailleurs de la Jeune Garde

</center>