When I right-click on the audio icon (in my desktop panel) I can set audio to "Mute": now, even if I set it to mute, it remains empty, nothing appears inside the square. You can see an example of this problem in the screen that I attached. I have this problem wherever there is a box like that (for example in the Update Manager under the voice "View" etc...). Is there a way to fix this? 
PS: the functions work, the only problem is a graphical problem
