I believe this is a known bug.
This is due to a lacking
argument in the Exec entry in the desktop file. In fact, the Freedesktop
(http://standards.freedesktop.org/deskto ... 01s06.html
that with %f, the system should assume that the application can't manage
multiple files on its command line, and should run multiple instances,
whereas with %F, all files can be pushed to the same single instance.
It's fixed from version 1.07, but Entropy, as well as Portage provides only version 1.04
You could request a version bump to 1.07 or latest: 1.08