If you use an external display rotated to 90 or 270 degrees and you enable video mirroring on that display, you may notice that Front Row doesn't present as expected. Instead, you see a black screen on the external display.
If you need to use Front Row with two displays, either use extended desktop mode or rotate your external display at either 0 or 180 degrees.
Click here for more information about the display rotation feature.
This document will be updated as more information becomes available.