Very likely its an issue with the EDID from the TV HDMI connection combined with a compatibility issue with the display driver or the TV is doing something weird.
1) Check your resolution options in XBMC does it offer 1920x1080@50Hz or 1280x720@50Hz etc if so try those.
2) try the alpha 9.11 release and see if the problem persists (though this has its own bugs)
3) Report the problem in the
XBMC Live forums and see if anyone can offer a permanent solution, if its a TV problem then nows the time before the next official release.