Actually you are not alone. If you select to boot in software mode ( cinnamon 2D ) it works as it should. However if you try to use the accelerated mode ( cinnamon ) it does not work properly at all. I don't have Mate to test this on but cinnamon does not work with the VBox accelerated drivers and multi-monitors.
You should post a ticket at bugtracker
and be sure to let them know that it has to do with 3D acceleration and post the guests log file as an attachment to the ticket.