key command "M" doesn't work in KEY EDITOR

Hello! I before worked in Cubase 4 and all functions worked very well but later in next versions of Cubase
I noticed some errors(
Why you cleaned the convenient Key commands? for example - key “M” doesn’t work in KEY EDITOR like mute track.
it became very inconvenient!
Please return and correct such errors with updating.

+1
at fact this global ‘M’ is missing from version ‘6’ … I think