Spline extruded meshes wont light map correctly?

I have been using Datasmith to import several interior models. Typically everything works great. Except the walls, these are usually modeled as a spline with an extrude modifier, they never map the lightmaps right. They behave as if the normals are flipped when they are not.

I have tried:

  1. Unify normals
  2. Custom UV maps and unwraps
  3. Re building them in smaller chunks
  4. Duplicate them
  5. Tessellate them
  6. Shell them

To no avail.

What usually happens is some faces map the interior light and others map the exterior light, as if the normals were flipped

Any help would be appreciated.