Screenshots can't be taken with "PrtSc" key when a context menu is opened. A user should be able to take a screenshot using his/her "PrtSc" key regardless of any focused context menus. I know that I can avoid this by setting a delay, still, this a required improvement. Xfce 4.12 on Opensuse Leap 15
See: https://bugzilla.xfce.org/show_bug.cgi?id=12323#c9