Without seeing the file, I would guess that some Walls were drawn in one direction (eg, left to right) and the others were drawn in the opposite direction (right to left). That presumes that all of the Walls have the same justification.
Did the Walls all have the same Wall Style prior to changing them to the current one? Did the Walls all have the "outside" on the "outside" (assuming that the original Wall Style had more than one component, and the outer component on one side was (visually) different from the one on the other side)?
If the Walls were originally of different styles, but all had the exterior side appropriately oriented, if the original Wall Styles were defined with the exterior on opposite sides relative to each other, then you would need to reverse the direction (or use Left justification for one and Right justification for the other) to get the exterior of both correctly oriented. Changing them all to one style would then result in what you see.
If the Walls were originally of the same style, but the style only had a single component, or had visually similar outer components, then it would not necessarily be obvious that some segments were reversed from others (particularly easy to do with the Center justifcation), until you changed the style to one with different exterior and interior components.