Brief update.
We have a repro only on one system to date (MBA), but it's reliable. All the other systems we tested don't show the issue. Might it be connected to the Intel GPU drivers? Does anybody see this with AMD or NVidia (in high performance mode if dual GPU)?

We're suspicious since this appears to be system specific so we're going to remove any custom behaviour out of the DL SW to see if we can actually affect the issue.

In the meanwhile the most effective workaround is still the same: don't let those pixels go to waste and use the Mac's screen as an auxiliary screen.

Carlo

Thanks for the update, Carlo!

My system is a MBA.

Thanks!
-Jeff

Can us MBA folks get a fix?
 

As I posted back in March and others before that, this problem is a killer on the 2011 MBA's. Any chance we can get a fix for that in the meantime? I'm getting tired of rebooting a couple of times a day as I switch between displays at home, work and when I present using the VGA adapter.

Please? I'll happily beta test it if you'd like. Reach out! :)
mike

Ok so now that we have a reproduction everything is a bit easier. We've been able to reproduce in the same conditions with another unaccelerated frame buffer product and with a basic frame buffer without any of our magic.

Everything points to a bug in the driver for the HD3000 graphics card, we opened bug 11655548 with Apple: you are welcome to push with them for its resolution.

Regards
Carlo

Thank you for the update Carlo!

I called Apple Support and gave them the bug report number and made it clear that I'd like to see it fixed. We'll see what happens. I suspect that by the time Mountain Lion comes out (which I hear the bug is not in ML), I'll probably just update to that.

Fixed in Mountain Lion
 

Just wanted to report some happy news on this nearly year-old problem: This appears to be fixed in Mountain Lion. I installed 10.8 yesterday, and I'm no longer seeing the phantom third screen. Hooray!

Yaay! Are you seeing the kernel panics that other users are reporting?

Great news:). Thanks for reporting it.

Yes, but all in all, they're infrequent and less disruptive than having to reboot multiple times per day.