ok intel graphics user doesn't have this problem so it seems it is potentially occurs with nvidia graphic cards. (both with nouveau and nvidia proprietary drivers). Added those packages to the issue.
** Also affects: nvidia-graphics-drivers-304 (Ubuntu) Importance: Undecided Status: New ** Also affects: xserver-xorg-video-nouveau (Ubuntu) Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to nvidia-graphics-drivers-304 in Ubuntu. https://bugs.launchpad.net/bugs/1497806 Title: Mirrored display broken in Xubuntu To manage notifications about this bug go to: https://bugs.launchpad.net/xfce4-settings/+bug/1497806/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp