Double-luck for Marverni, then. That was my strongest province; you would have been facing around 160 defenders, including more Steel Warriors than were in the actual battle.
If you'd lost that battle and the originating province your entire force would have disappeared. That is actually what I was hoping for.
Check the main forum for this possible bug:
http://www.shrapnelcommunity.com/thr...b=5&o=&fpart=1
Wonder if it is a possible terrain constraint? River between the two territories whose forces bounced...not sure if others experiencing this were trying cross rivers.