The system tray correctly appears when updates are available, but does not disappear after updates have been applied. 
When clicking on the system tray icon after the updates have been applied, the the popup window shows the same message as the initial one , i.e. the number of updates available and an enabled "Update" button.

Reproducible: Always

Steps to Reproduce:
1. When new updates are available, use muon updater to install them.
2. 
3.

Actual Results:  
After the updates have been applied, the system tray icon is still available, and when clicked it still shows the same number of available updates, and the (enabled) "Update" button.

Expected Results:  
The system tray icon should disappear.