maybe it got shorted out or something... really weird. I can say though, that the video out can be a little sketch from time to time. I have always had better luck with the Mac OS X video controls over Apple's boot loader. Its only going to boot onto one screen, regardless of how many are attached. Maybe its still defaulting to the primary display; guessing that its extending and not mirroring...
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"Fix it 'til it Breaks."

Jacob - EiC & Director of Technology
Mac Pro Quad 2.66 - 4GB RAM
160 GB SATA RAID 1 - 650 GB Storage
Quad 19" Widescreen LCDs
Accessorized to the Hilt