I have a friend that recently purchased an 01 740i M Sport with the same thing occurring. It has the electrochromatic side mirrors and the passenger side is a pinkish gold tint and the driver side is perfectly clear. We were just wondeing about this same thing and the cause as well. With his, both side mirrors tint as they are supposed to so that leaves me to believe it is an issue with the glass itself and not the electrical side.