That's weird, In my testing that's never happened... I don't know what to tell you. When I test (or in the case, tested, I am inactive at the moment)models, I always have a few days of trouble shooting, because of weird animation issues, but I've never had a texture mapping issue where when you rotate it its a different texture, the back of the stop sign should be gray. if its not, umm.. I'm not sure what to tell you, but I am incapable of fixing it at the moment.
~3rgytr54