I see werner has now recessed the button in the adjustable ferrule so it can't accidentally be released. This prompted me to fit the button covers Werner supplied for the old-style shafts on which the button could be knocked.
I'm trying the glass blades as an alternative to the carbon foam core to see if they're more gentle on my left shoulder, which still has a few problems.
It would be nice if I could be retrofitted with a solution.