I'm running Ubuntu 18.10, and went to adjust the volume after a clean install before (first time installing Spinnorality on this machine). The button on each of the sliders doesn't stay under the mouse. For example, if I want to turn the master volume down to 50, I intuitively grab the volume control button, which defaults to the loud extreme, at 100, and move my mouse to the center of the slider, where I expect 50 is. The button doesn't follow the mouse correctly; instead, it shoots to an extreme around 20, much softer than I wanted.
While playing around with this, I noticed that if I move my mouse vertically while dragging one of the slider buttons, so that the mouse intersects another slider button, both buttons move together. In fact, I can move all the slider buttons simultaneously, which feels wrong, since the options are unrelated and it's possible to do by accident.
This is clearly a low-priority bug, as it doesn't interfere with the actual gameplay in any way.