Q: CAUTION: Screen Cloning with Filevault & EFI password can brick your Macbook

I used screen cloning in 10.9.5 while connecting my external display (1920x1080), then switched off the external display, closed the lid on the Macbook, letting it go to (Suspend To Disk) power saving, disconnected the external display and after a bit, tried powering up the Macbook.

Now it appears that there is an incorrect screen resolution set for the internal display on boot (the scaled 1920x1080 mode instead of 1680x1050), which prevents the system from booting after the Filevault logon screen. Instead of the desktop appearing, the internal display stays blank after the grey screen/cogwheel, and connecting the external monitor only shows coloured vertical bars.

It is impossible to reset the PRAM because the EFI password is set, which cannot be removed since it is impossible to boot into Internet Recovery or any other boot medium such as DVDs or USB devices.

Due to Filevault being in place, Safe Boot is also impossible.

As such, the Macbook is practically bricked. I highly recommend disconnecting any external monitor before letting your Macbook go to sleep!