`_on_button_released` handler of `SmoothScale` is not called

The _on_button_released method of SmoothScale does not seem to be called when the user releases the button. I verified this by inserting a simple print statement into the _on_button_pressed and _on_button_released handlers, and only the _pressed one actually prints.

I noticed this because I am writing a music player myself, and I had some trouble with my progress bar myself, so I wanted to see how other implementations deal with this. When I asked about my problem in a chat, I was linked to this line as a source of this behavior.

I am not sure if or what impact this actually has on the functionality of the application, but I would be interested if it's possible to fix.