OK, if Displays shows two rectangles that means XMir somehow thinks it's in multi-monitor or clone mode. And in multimonitor mode it's a known bug that there will be lag and funny glitches on one or more of the displays. That's bug 1216472, for which a fix is landing soon.
OK, if Displays shows two rectangles that means XMir somehow thinks it's in multi-monitor or clone mode. And in multimonitor mode it's a known bug that there will be lag and funny glitches on one or more of the displays. That's bug 1216472, for which a fix is landing soon.