When running MythTV under Ubuntu, the top menu (panel) may appear over MythTV’s output. The panel can be set to auto-hide, but even when hidden, several pixels will be displayed to remind you of its presence. Luckily, the number of pixels shown can be customized.
Select apps | panel | toplevels | top_panel_screen0.
Check auto_hide, if you haven’t already turned auto-hiding on.
Set auto_hide_size to 0 (or whatever number of pixels you want to be displayed in “hidden” mode).