Rhythmbox unity launcher icon Quit action won't work - Howto quick Quit

16.04 here

I also tried to add this action to ~/.local/share/applications/rhythmbox.desktop but it is unsuccessful (with an additional dedicated Quit section exec=rhythmbox-client --quit and name=Quit plus Quit; action in Actions line) with weird side effect*.

Once Rhythmbox is running, eventually reduced, even I have previously set the launcher icon to "Keep in launcher", then the icon looses the focus indicator (small arrow on the right) as intended, and there is no more a way to quit Rhythmbox with a simple right-click. The ~Active window indicator~ (small arrow on the left) although remains, at least until I Alt+F4 or click the Close window button when the Rhythmbox is opened. When I want to quit Rhythmbox I first have open the window and then only I can Ctrl+W, Menu File/Close, so the single way to stop is from the application menu which is heavy boring.

*[EDIT]: new Quit, Close, Exit or Stop actions won't show a new item in icon context menu, as if they were reserved keywords all tied to the default Quit action we have for all other active application icons. Although, I reached to have a new item displayed for exec=... --quit as long I give another name, e.g. "Die" or something in my own language, then only I have a way to quick quit when the default Quit item disappeared.

Whenever I reach to add a working Quit action, then I get a several seconds hourglass in Unity launcher and syslog reports things like:

Jun 18 13:27:40 nux org.freedesktop.Notifications[1832]: ** (notify-osd:2149): WARNING **: stack_close_notification_handler(): notification id == 0, likely wrong
Jun 18 13:27:44 nux gnome-session[1963]: ** (zeitgeist-datahub:2879): WARNING **: zeitgeist-datahub.vala:212: Error during inserting events: GDBus.Error:org.gnome.zeitgeist.EngineError.InvalidArgument: Incomplete event: interpretation, manifestation and actor are required
Jun 18 13:29:19 nux gnome-session[1963]: message repeated 2 times: [ ** (zeitgeist-datahub:2879): WARNING **: zeitgeist-datahub.vala:212: Error during inserting events: GDBus.Error:org.gnome.zeitgeist.EngineError.InvalidArgument: Incomplete event: interpretation, manifestation and actor are required]

...
Jun 18 13:39:49 nux gnome-session[1963]: ** (zeitgeist-datahub:2879): WARNING **: zeitgeist-datahub.vala:212: Error during inserting events: GDBus.Error:org.gnome.zeitgeist.EngineError.InvalidArgument: Incomplete event: interpretation, manifestation and actor are required
Jun 18 13:40:19 nux org.freedesktop.Notifications[1832]: ** (notify-osd:2149): WARNING **: stack_close_notification_handler(): notification id == 0, likely wrong

Sometimes I have to select the action twice so that it executes: first time the focus arrow disppears, second one the app stops. It seems like the icon is no more bounded to the running application, although rhythmbox-client is stated to "controls a running instance of rhythmbox" according to the manual. Instead, the action seems to target the icon itself, just killing the window and not ending the app... sorry for my wording, I'm not native englih speaker.

Also I don't understand how English strings in the file map to translated items in the icon menu.

Please could you tell me advises to workaround this locked behaviour, I'm out of imagination. Many thanks in advance.