Comment 1 for bug 39428

I have this exact same problem (using Ubuntu Dapper, up to date via online repositories). I tried creating a new "test" user, and logging in as that user, so that the default Ubuntu desktop settings would be applied. But the problem still exists for that user.

On a folder in Nautilus, my right-click menu shows (among other things):
Open with "Filelight"
Open with "Konqueror"
Open with Other Application...
If I choose the "Other Application" option, I can select "XMMS music player" from the list, and that works (plays the music files). But this application is not remembered in the "Open with ..." choices in the right-click menu.

Also, instead of choosing "Open with Other Application...", I can choose "Properties" from the bottom of that menu. This brings up a tabbed dialog. The "Open With" tab lists the options I can use to open a "folder":
Filelight
Konqueror
Open Folder (this option is selected)

Clicking the "+ Add" button is also ineffective at adding "XMMS" to the list of options.
And clicking any of the two non-selected items fails to change the selected item - the radio bullet will not move from "Open Folder" to any other bullet-hole.

In summary, it behaves as if the list is somehow "read-only".

I wonder if this bug is a duplicate of #35463 ?