Thanks for the feeback.
I cannot click on the icon again because it is hidden behind the volume control window.
I moved the toolbar from its default placement to "top center" after installation.
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Update: The window disappears when the toolbar is in its default "bottom center" position.
Drawing the window below the toolbar (if located at the "top center") will fix the issue.
Or just enabling the window to be cleared after pressing ESC will fix the issue too.
How can I submit a bug report?