Originally Posted by ensiform
Do not use nodraw on brushes that are meant to be solid. Use caulk on faces that are not to be seen. Nodraw is non-solid and it generally uses a specific side of the brush to determine whether the entire brush is solid or not (its not always the same).
I think its that the wall is supposed to be non-solid but it turns solid.
What version of gtk are you useing and is it the latest release coz you get bug fixes and stuff that makes it much more reliable. I've done a similar thing with the latest release of 1.5.0 and it has worked for me.
Its proberably just one of those things so you could always try re-installing radiant.