Strange thing: In my standard page format template I inserted a custom background-image for testing. After testing was finished I applied colour None to the page format template and deleted this background-image from my disk.
If I now edit the standard page format template and click on “Organize” (Verwalten in German) the file name of this image is still listed as a background-image. Next I applied a default background and applied None as background again. If you close the standard format template and edit it again the name of the background is still listed.
In fact you cannot really deselect a selected background-image. Coming back to the strangeness: If I save the .ott as .doc the background-image is visible although it is unvisible in the .ott.
Any ideas how to really remove the background?