The B&N magazine format is a proprietary extension of EPUB that is not supported by other reading software including calibre. It uses a replicaMap.xml file that links to page images and also provide links between articles and pages.
You should be able to see the replicaMap.xml file and the images it links to in the original EPUB from B&N. Because calibre is unaware of the extra files involved, if you attempt to convert a B&N magazine to another format all of the extra files, including the page images, will be removed.
Added: Link to more information on this format:
The Barnes & Noble Fixed-layout Format