Addendum: It occurred to me that since the taskbar was wiggin' out, that'd be a good first place to try troubleshooting.. I semi-colon'ed out the netloadmodule command that called taskbar3 in the theme.rc.. No taskbar loads, but the !ShutDown command works properly!

So it seems to be a problem with taskbar3-0.306_alpha-3.

I've re-enabled the call for taskbar3 and I've found that the shutdown menu shows properly if the taskbar is hidden - the problem actually only occurs if the taskbar is shown. This means that I can use the hotkey to hide the taskbar before using the hotkey to shut down, but that's just a work-around for the problem.

What would be ideal would be an actual solution to the problem as it might help in future applications where this might crop up and not be so easily worked around...