Quote Originally Posted by The Errant
Given pathfinding seems to have trouble making troops on walls flee down a tower or ladder this might be a related issue. Can't remember if vanilla RTW had this issue though.
It's a vanilla bug, although one that seems to have been introduced by the 1.3 or 1.5 patch. IIRC someone posted a fix about a year ago, but other people reported that it didn't work.