Tis an ancient BMW tradition the self ejecting bag, going back at least to Airhead days, when the standard precaution was a stout leather belt and buckle around the bag and mountings to hold it in place when the inevitable happened.
'77 Harley Ironhead 6,000 miles across Oz
Reryder (AKA Hopper)
1977 Harley Sportster
01 HONDA VFR800
Ancient Harley 45, Snortster (Sporty engine in a Norton), Norton Atlas, Honda 350/4, Ariel HS scrambler