When a package is available from multiple apt repositories, it shows up multiple times in app lists. All the entries take you to the same page showing the same latest version, and all the deb repositories are marked as currently active in the "Source" popover.

As an example: evince is available in different versions from amber, amber-phone and amber-phone-staging right now, which makes it appear three times.

This also happens on the main page with stuff like "Editor's Picks" (currently it's just filled with Evinces for me :P)