I've also ready where the driver had a manual slider, but was too lazy to get out and slide it backward. The result was a dent in the 5er and a broken glass. I've also read where the driver had an auto slider but it failed to do what it was intended to do and the result was a dent in the 5er and a broken glass.
I have the 5er that will not make a 90* with my truck. I opted away from any slider and take nothing for granted, so now, and always have had my wife stand beside as spotter for any closeness that happens. We haven't hit in 9 years, but it could happen just as it can and has happened to others with a slider of some type.