I had a similar problem with a Volvo seat a few years ago. For some reason the cable was too short for the cable housing. I just cut the cable housing so that there was now way the cable could slip back and disengage itself. I had no problems for the next 3 years and the current owner (one year) has not had any problems. I don't know if you can cut the cable housing on your seat, but if you can that would be the fix.