Does it still work for you if you go to the conductor window and check "enable qwerty keys..."?

I believe that's what happen. Before Build 463 the keyboard shortcuts (ALT 3, ALT 4, ALT 5,...) to turn off an instrument would work no matter if "enable qwerty keys..." was checked or not.

In build 463, the keyboard shortcuts do not work if "enable qwerty keys..." is checked in the conductor window.

This bug has been reported to PG music.