We are using a Qt-based surface for drawing the music to the screen, and this is a bug caused by the lack of floating point precision in its QPainter raster device (details here). Unfortunately at the moment the Qt developers have not yet shown any interest in addressing this problem, and although it is within our power to get our hands dirty and fix it ourselves, we would rather spend our time developing the application itself where possible. The problem only manifests on non-Retina/high-DPI displays, but all the same we do want to see it fixed.