check thread here:
http://nolanparty.com/mediaportal.sourceforge.net/phpBB2/viewtopic.php?t=2372
Going from Fullscreen to GUI and back to full screen again fixes it (press X twice)

- start MP
- start My TV
- switch to fullscreen
- hit "y" for OSD, it appears, close it again with "y"
- switch channel, using F7, F8 or the numeric keys
- hit "y" for OSD and nothing will appear (but it is there)
- also the OSD for numeric key entries is now broken

Sometimes closing fullscreen, sometimes closing My TV solves this.