We all get the same problem and the same issues returned.
I guess its related to the paint internal, paint external walls modes but maybe not.
Not quite sure why we have that but thats the way its designed.
As a result I sometimes end up with 3 section thickness walls - one inside, one outside and one in the middle so where that one comes from I have no idea.
Not sure why we need all that at all or what it does to the game speed and file size as I presume that 3 walls for every one means 3 times as many polys as needed.
Why we cant place a single wall (of a specified thickness) which has one texture one side and one on the other and leave it as that I dont know. But there you go - the wonders of FPSC.
The whole issue of this wall complexity which seems to be unecessarily complex - including the problems of texture inheritance, flickering textures and the corner issue could do with some attention from the developers.
Unfortunately TGC seem to have so many requests for improvements to FPSC for us to expect to see many of them becoming a reality.
Ah well.
"I am and forever will be your friend"