Ok, I think I see the problem. It works for me because I have those scenes in a common widget in QLC+ that guarantees that there is only one scene active at the same time. When I remove the widget, it works the way you described.
I'll provide some changes to the way Sound Show works with QLC Functions. I'll try to provide this new version as soon as possible. In the meantime, you could have a workaround by creating a widget.
Sorry for the inconvenience and thanks for your feedback