If you chose to display a OSD Background graphics the TV output in the player will be displayed in a small preview window. If no background image is to be displayed the TV output in the player window will remain in its full size behind the OSD display. Follow the advice of the author od the skin that you are using if Display Background graphics should be enabled or not. In order to use a background graphic the skin actually needs to have a space reserved for it in the menus. The preview window used when displaying a background image might however introduce some inconsistencies, like for example when it comes to OSD overscan or changes in the aspect ratio.