Sometimes when working on something an old screen with Windows, that are no longer open appear. I can see that it is something that I have been working on in the past and I have to move my cursor or open other windows/menus to get the screen to refresh.
This seems to happen more frequently, but not exclusively with VirtualBox.
I'm running a fresh install of Xubuntu with pretty much only VirtualBox installed afterwards and started it on a brand new PC, so there shouldn't be a hardware issue.
Could VirtualBox be the cause?