First of all, authors decided there's no need to have north AND south wall for each square tile. South wall actually is the north wall of southern tile.
Second thing, they needed to implement outer walls, which are simple walls with one exception - they are protruded to one of sides, so there are 4 outer walls types. Since they are limited to 16x16 (one loft slice) and cannot go outside of this square, they have to use other tiles, and they have chosen to use "object" tile as north and west outer walls. And by the way, there is an issue with inner "panels" and outer walls being adjacent.
Because of this units are unable to stand near these walls, and this is real gameplay flaw which have to be eleminated. And maps are "hardcoded" to be as they are, without a chance to be rotated.
The way of eleminating this is:
1) Implement "diagonal" wall flags for wall object MCDs (to make them passable by diagonally NE/SW or NW/SE).
2) Implement different map format, which will have 4 walls per tile, not 2.
3) Implement "rotated tiles" table (4 tile IDs for every direction of every tile).
4) Update very map block to fit new map format.
5) Ask Daishiva to update his map editor for handling new map format (which obviously will be in text-form)
6) Fix UFO ship maps and base blocks, and change every outer "object" wall tile to "advanced" wall tile and make them symmetric (computer screens and panels not only for 2 walls, but for 4).
7) Update functions of walking and pathfinder to handle these changes. Update renderer to handle 4 walls per tile (render order must include south and east walls after others).
After these changes map blocks could be rotated for any of 90/180/270 degrees direction, and units could be able to move along any of outer walls. And battlescape view will be rotatable as well.