I posted this on the Problems section, with little response. Now it appears it's happened to at least three of us. Yes, the cure is to re-bind it - even though in the key bindings window it says it says it IS bound. I also had the same with "I" for Inspector. "M" was ok.
I would add that I'm not a 'system tinkerer' - my W10 64 bit system has been unchanged for months, nay, years except for moving from W7 to W10, and the only variables in my case are W10 updates and Sonar updates.
Cakewalk - can you take note please? I don't think a blip like this should be taken lightly. Could be an indication of something more serious festering away in the code? I'm a bit peeved that we often see pledges by CW to concentrate for the time being on fixing things, only to find a new cockup appears which itself needs fixing in a later release.