Comment 14 for bug 1313291

Michael: yes, booting with the external screen connected solves the problem.

t-lo: screen mirroring works, but is not always a good workaround. The aspect ratio of internal and external screen might not be the same. You are also limited to screen resolutions that work on both screens (e.g. for me this means no HD). Better than nothing, of course, but not a real solution.