Comment 9 for bug 854382

@Colan Schwartz: thanks for the link. It suggests a workaround for the issue: start simple-scan from terminal with `XDG_CURRENT_DESKTOP=XFCE simple-scan` (each time). I confirm this is harmless (it doesn't change anything on your system so if you retart simple-scan as usual it won't work) and works under Ubuntu 18.04 (Ubuntu desktop). This seems to indicate that the problem comes from the integration with the desktop.