Two pages are always output by scanning both sides through PaperStream IP (ISIS). As both sides are merged into the first page when specifying "Double-page Spread" for [Carrier Sheet] or [Front/Back Merging], the second page has no image to show and a blank page is output as the second page.
To remove a blank page, enable [Blank Page Detection]. Refer to the Help file for the models that supports [Carrier Sheet] or [Front/Back Merging].