these days they make them float for safety - and of course mostly to irritate the passenger with the backrest jogging back and forth, check out the 1300GS... after years of killing policemen on the A3, KTM worked out if the panniers float, the bike doesn't weave, so BMW did it to the topbox
as for your install which top box?
somehow the halfwits think differently - the vario will stay on under braking but falls off on acceleration with passenger load - so you lose them too. Whereas givi has these toy locating fastenings at the front that aim to hold it for acceleration but then almost has nothing under braking - so the rider gets a get a quick thrill when stopping hard
the vario one wobbles and rattles, even earlier ones had a different catch... not really liking the hope it fastening any of them came with - one for safety, don't need her complaining when she falls off the back - but mainly an anti-theft idea, at the cost of these - the std plastic lock install wasn't my cup of tea - as a one pound shop screwdriver gets you a bonus £700 topobox - so in a shocking step back in time I used the grown up bolt on feature and now it doesn't rattle either - if you check underneath in the middle - there's a place to get the bolts through on the black bracket it pretents to clip on - almost as if they once intended to mount it safely!
the baby aluminium thing has a far more secure fastening to the bike, but you want that stolen - so you can buy the twin helmet size it always needed -
aftermarket givi with the monokey hope it stays attached quick release joke plate fastening, is a combo of two appalling designs above - fortunately the same bolts that can hold the vario box on work perfectly for the givi box too, you just have to get creative with some spacers !
