xdg-open fails to open PDF attachment

[Robin Green <greenrd@greenrd.org>]

On my system (Fedora rawhide), something (not sure what) has
configured my system so that wanderlust opens PDF attachments with the
xdg-open command. This is a general-purpose command which I think has
something to do with the Open Desktop interoperability initiative
between KDE and Gnome. Anyway. That's an aside.

The problem is, it doesn't work, because xdg-open calls the PDF viewer
okular, which runs in the background (incidentally, on another
display!) and xdg-open then quits. After that, the temporary file is
deleted (presumably by wanderlust) so okular can't open it.

Now, this is a head-scratcher. Is this a Wanderlust bug? An xdg-open
bug? Or a Fedora configuration bug? Or none of these? I don't even
know what's causing xdg-open to be used, so I don't really know where
to start.
-- 
Robin