Walls and floor are flush.
Happens with or without the trim brush.

Map Source Download (Sendspace)
I have no idea how to bundle Radiant materials, so unfortunately you'll have to compile the materials yourself to see them in Radiant. A .GDT source file is included, you won't be able to compile the models but they are not necessary.

I'd like to know how to fix the skybox showing, along with what I need to copy to get the textures to show in Radiant. (Materials, or material_properties?)