My understanding is that it's a wallpaper mask over a filled (#ffffff) background. Selecting the 'None' button only tells it there's no tiling to the image selected. If you clear the image url or click that left box there should be nothing to tile.

This example you have says to me that you have an image input, grey linen and it's tiling is none, leaving one image; opposed to tiling it vertically or horizontally or both. Where that image sits as a single tile makes it look like a partial border. Removing that single tile should give you the results you're asking. I can't foresee any impacts from this on the printing margins.