Something to note:
If there is ANY militia or troop presence left in the city/townsland, then the region owner is the defender and will always get the walls in defense, even if the attacking realm has won the last few battles and should, by rights, be cozily set up in the castle. Hence why hunting enemies is so vitally important - if you leave scattered forces in a region, and they rally just before a counter-attack, your troops will be the ones attacking.
If you start a TO, and there is zero presence of enemy troops, militia or otherwise, you should be set up as the defender and get full use of the walls.
Otherwise, if you start a TO, neither side will get the walls since both sides are defending.
