Originally Posted by Chris142
My uneducated guess is that the elements expand when they get wet. And with nowhere to go they bend and twist. A regular can style of filter has only a spring on one end so they can expand and stay "normal" looking.
Cartridge filters, at least some of them (I don't know about this BMW application.) have a spring applying force to one end, too. The range of spring travel should take care of reasonable manufacturing tolerance variations in the filter length, or slight filter expansion. Of course that won't work if the filter is grossly too long, or if the spring exerts more force than the cartridge can withstand.