I suggest that you remove/disable xfce4-power-manager and test again.
Furthermore, we need details about your GPU + used driver. Please attach the output of "lspci -v" to this bug report.
I suggest that you remove/disable xfce4-power-manager and test again.
Furthermore, we need details about your GPU + used driver. Please attach the output of "lspci -v" to this bug report.