@rolfy
I think I have figured out the cause of the flickering, actually the destructive part of the wall clashes with the wall of the segment which is on the other side of the corridor

for example I put "chateau study room" so when the wall is destructed you get access to this room, the solution was to remove the wall in "chateau study romm" which is just opposite to our destructive wall and voila there is no clash anymore.
Here is a photo a of the editor window which shows the clash, as you see the destructive wall clashes with the texture of the opposite segment on the other side and you can see its texture appearing on our wall:
http://img15.hostingpics.net/pics/837507FPSCMapEditor.jpg
But the sole problem that remains is that the destructive part of the wall has no light/shadows effects on it! so when I put a light source in the corrior all the walls segments get the light effect except for the destructive part and this is ugly coz you can easily know that this part of the wall is not like others

so it has no more logic
here is a photo (I tested all the ww2 corridors, no clash anymore) but as you see in the photo we can easily distinguish the destructive part of the wall:
http://img15.hostingpics.net/pics/916690FPSCGame.jpg
My specs (Asus Republic of Gamers):
Intel core i7-267QM, 2.2Ghz
4Gb DDR3 RAM
nvidia GTX 560m 2Gb GDDR5
Thanks