xfce4-screensaver makes remote control trough x11vnc laggy after wake up and unlock remote client

When xfce4-screensaver is used on a machine with a x11vnc client, remotely waking up and unlocking the machine makes using the desktop tricky because the display is now very laggy.

Prerequisites : a) xfce4-screensaver installed and lock function enabled b) x11vnc package installed and started on the machine.

Steps to reproduce the issue :

1. On the client, wait for screen locked and sleeping.
2. Remotely wake it up through Remmina (for example).
3. Remotely unlock the desktop.

Results : The remote desktop is hardly usable Expected results : The use of the remote desktop should be smooth as it was before the remote desktop locked.