This works fine:

   yelp ghelp:gedit

But the following results in 'The requested URI "ghelp:gnome-volume-manager" is invalid':

   yelp ghelp:gnome-volume-manager

Seems like yelp looks only at the scrollkeeper files in /usr/share/omf/ to resolve ghelp: URIs. For applications that don't come with an omf file, like gnome-volume-manager, you can't open the corresponding help page with "yelp ghelp:app".

In openSUSE 10.2, yelp resolved ghelp: URIs by searching through the known help file directories for the application's help files.

I assume a number of applications invoke the "yelp ghelp:something" command when their "Help" meny entry is clicked. If those applications don't come with scrollkeeper files, clicking the "Help" button will now result in the aforementioned error.