Are you running the xfwm built-in compositing? I've found that, on a Xubuntu machine using xfwm and compositing, the desktop would be shown together with the "unlock dialog".
Expected behaviour: Lock screen -> move mouse -> black screen surrounding the "unlock dialog"
Seen behaviour: Lock screen -> move mouse -> the desktop surrounds the "unlock dialog"
Workaround 1: Disable compositing from the "Preferences" -> "Window manager settings" -> "Compositing" tab
Workaround 2: On the previous tab, make sure the second option (too long to remember) is unchecked.
Are you running the xfwm built-in compositing? I've found that, on a Xubuntu machine using xfwm and compositing, the desktop would be shown together with the "unlock dialog".
Expected behaviour: Lock screen -> move mouse -> black screen surrounding the "unlock dialog"
Seen behaviour: Lock screen -> move mouse -> the desktop surrounds the "unlock dialog"
Workaround 1: Disable compositing from the "Preferences" -> "Window manager settings" -> "Compositing" tab
Workaround 2: On the previous tab, make sure the second option (too long to remember) is unchecked.