I was seeing this bug in 13.10 but it seemed to not be an issue in 14.04 for a few weeks after I upgraded, but recently it started again. Maybe I had applied the workaround in 13.10 and it got carried over, but a post-upgrade update reverted it. Maybe.
The workaround has helped me: editing /etc/xdg/autostart/xfce4-power-manager.desktop replacing 'Exec=xfce4-power-manager' with 'Exec=xfce4-power-manager --no-daemon'
I was seeing this bug in 13.10 but it seemed to not be an issue in 14.04 for a few weeks after I upgraded, but recently it started again. Maybe I had applied the workaround in 13.10 and it got carried over, but a post-upgrade update reverted it. Maybe.
The workaround has helped me: editing /etc/xdg/ autostart/ xfce4-power- manager. desktop replacing 'Exec=xfce4- power-manager' with 'Exec=xfce4- power-manager --no-daemon'