Add to Playlist with URL broken

[Robert Sander]

When the play queue contains a web radio URL and I try to add that to a playlist (via right click "Add to playlist" or Copy and Pasting it to the playlist), the music player client always tells me that playlist editing is not supported.

Adding MP3s on the server to any playlist works.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: gmpc 11.8.16-6ubuntu1
ProcVersionSignature: Ubuntu 3.11.0-13.5-lowlatency 3.11.6
Uname: Linux 3.11.0-13-lowlatency x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.12.5-0ubuntu2.1
Architecture: amd64
Date: Fri Nov 22 10:45:25 2013
InstallationDate: Installed on 2012-06-14 (525 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
SourcePackage: gmpc
UpgradeStatus: Upgraded to saucy on 2013-10-29 (24 days ago)