I adjusted to a lower window resolution in the demo and it worked fine. It still doesn't work in full screen and various other combinations of resolutions push when it's windowed. In full screen regardless of resolution clicking on button does nothing and program needs to be killed externally to shut it down. Seems like it could be handled better... maybe even tested.
In windowed mode there are issues with various Ubuntu overlays interfering with the window. they can be fixed by forcing the window to be "always on top".
Complaints and bugs aside the demo was fun enough to justify a purchase. I hope some attention is paid to these kind of issues.