It appen that some icons in the notification area to not show the correct state, or even to go missing. It's a glitch that can affect any of those icons.
What I do in that case:
Press and hold Ctrl + Shift and tap the Esc key to open the task manager.
Find "Explorer.exe" in the process tab.
Kill it. (end process)
The task bar and ALL desktop icons will disapear, it's normal and expected.
Also, all keyboard shortcuts/hotkeys will also stop functioning.
Switch to the applications tab.
Click the "New task" button.
In the box that pop up, type "explorer" and click OK.
This will restart the explorer and, usualy, correct any problem notification icon, including erroneous and missing ones.
Electro, January 2016