Check all the plugs going into the seat and mirror memory module under the seat, maybe wires are touching. In case one of the plugs is broken, not all are available anymore, here is how you can do, I made a write up with p/n's and what is available and how to make them fit
http://www.bimmerboard.com/forums/posts/1236746/
I have read about some defective control units where the function suddenly worked in reverse.
Training manual SMM http://www.e38.org/e32/BMW_pdfs/smm.pdf