I agree, the behavior of the dedicated volume buttons when locked is incorrect. Any time the “locked” message displays, the controls are inhibited for about 40 seconds. The lock feature should not affect the hard buttons, just the touchpad.
It’s quirky that if the touchpad is not touched, or even the power button is touched, actually- as a brief tap of the power button will elicit the “locked” screen display, starting the 40 second inhibit all over again.
The threshold for the lock function is about 500ms (1/2 second). A brief press of the power button (above this time) will toggle the lock on or off. If the button is merely tapped, the “locked” screen displays. Obviously, there’s a little learning curve here, but it’s not so bad overall.
If the volume buttons are operated after about 40 seconds, they work normally when locked.
Bob 
