Already tried it. No success :(

So odd, power management events work when the mouse is unplugged, the computer is locked, or no profile is signed in.

It's simple: remove the Intellmouse software.  You'll lose the tilt wheel gimmick, but get your power mgmt back.  It worked for me.

Is it possible that there is some imperceptible (to us humans) movement going on which resets the timer?  In other words, loud subwoofer or footsteps walking past the table your mouse is on?  Can you try setting your laptop up in an unoccupied area of your home to see if things work differently there?

I preview a screensaver, and the screensaver is not disturbed.