On macOS 11 beta (BigSur) when running the SwingSet2 demo there
are artifacts on the background of whatever is the selected toolbar icon
when using the Aqua Look and Feel.
Grey rectangles appear to be incorrectly positioned/stretched in both
x and y directions. See attached image and look at the icon for
the combobox demo.
This is not specific to SwingSet2. I noticed similar issues in J2Demo.