This occurs for me with both TNGv1 and TNGv2 on multiple computers, so I think it might be a small bug. If you open the settings dialog and change to a different desktop (Ctrl-Start right arrow etc) you get this strange artefact on the other desktops.



This weird window outline is exactly where the settings dialog is on the other desktop. Not a biggie, but it had my going wtf for a while.