Probably what happened was that, although you removed the material, UV map was still there for that building. If you leave any UV definition on your object, object will go white like your screen shot if you have Textured View Port shading. Rendered image will be as it should be.
This is the fuzzy organization I never liked between object and UV map. It is hard to tell if object have UV map on it or not. And there is no “UV remove” button!
I think this one goes a little deeper than that (ie into bug territory). The project I reimported the meshes to didn’t have a texture anywhere, not on the materials, not in the drop down menu in “UV”, yet the viewport shading in textured mode was acting up like in my screenshots.
I agree, UV shading in blender 2.4x isn’t exactly straightforward. It’s much better in 2.5 but I’m not keen on the fly and sculpt modes in 2.5… but then it’s still in Alpha I believe.
But anyway I was able to solve it by exporting to .raw. That did away with it.