Stuck in 4:3 aspect. Can't get back to 16:9

[Mugsy]

I have a widescreen monitor with pivoting stand. While in pivot/portrait mode, I opened the WMC Guide and the window resized to fit the new screen width.

Back in normal Widescreen (landscape) mode, WMC is stuck in a 4:3 window. Resizing by width also resizes by height so it remains stuck in 4:3 mode.

I've tried rebooting. I have "/wide /mcesuperbar://tv?live=true" in my WMC shortcut to automatically launch Live TV in a widescreen window.

I've tried going through setup and setting the monitor to 16:Nine (why can't I type the digit?) Widescreen, but it didn't help. Altering "Zoom" didn't help.

Once upon a time, I remember having a bat file (or reg file) that would fix the issue, but I can't find it now.

Anyone know how to fix this? TIA.