(continuing from previous post)
adding gmusicbrowser to the whitelist solves the problem
gsettings set com.canonical.Unity.Panel systray-whitelist "['JavaEmbeddedFrame', 'Mumble', 'Wine', 'Skype', 'hp-systray', 'gmusicbrowser']"
actually it seems you should add manually every program you want in the systray. Otherwise the systray doesn't work correctly.
(continuing from previous post)
adding gmusicbrowser to the whitelist solves the problem
gsettings set com.canonical. Unity.Panel systray-whitelist "['JavaEmbedded Frame', 'Mumble', 'Wine', 'Skype', 'hp-systray', 'gmusicbrowser']"
actually it seems you should add manually every program you want in the systray. Otherwise the systray doesn't work correctly.