I think even if any of the above did cause his car to open, BMW is still liable. They should design their product to withstand this sort interference, particularly since the car is likely to experience all of the above. Customers shouldn't be the test lab for BMW, they should have tested for all likely interferences already.

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2010 X5d, Space Gray, Tobacco, Premium, Tech, and rear climate packages, roof rails, spare tire, and iPod adapter.
2006 330i, Sport, 6MT