http://www.supremecourt.gov/opinions/10pdf/08-1314.pdf
Court: Family can sue Mazda over seat belt death - Yahoo! News (http://news.yahoo.com/s/ap/20110223/ap_on_re_us/us_supreme_court_seat_belts - broken link)
"The Supreme Court will let Mazda be sued in California courts in case involving a woman who died while wearing a seat belt across her lap in her family's minivan. The high court in a unanimous judgment Wednesday agreed to let the lawsuit go forward, despite complaints from the car company that federal regulators gave it an option on whether to install lap belts or lap-and-shoulder belts in the middle seats in the back of the van."
Mazda, following government regulations, can be sued for having a lap-belt in the middle of the back seat instead of a shoulder-lap belt. As near as I can tell, there is no complaint that the belt was non-functional or poorly designed.