When I flip my screen and put my Duo in tablet mode, my Duo will power off after about ten seconds. I have set the close lid power option to do nothing. It boots and runs fine when in laptop mode. I am dual booting Win 8 consumers preview and Win 7 and it happens in both operating systems. It also doesn't matter if it is docked or not. About every 7 reboots it will power on and work just fine in tablet mode, but then Windows 8 will spend half an hour attempting repairs.
It already went back to Dell twice for a bad motherboards, and now is out of warranty.