I see this all the time when I alt-tab to the desktop and come back.   Others have suggested playing in window mode to temp overcome this defect/bug.  

Even though your computer is set to do nothing it is probably still turning off your monitor?   This cases a Direct X mode change (pretty sure?).  

I agree that it should not work that way, but I was hoping that windowed mode would help you play in the mean time.

It you do a quick google it looks like several applications battle lid closing if they utilize directx - including VLC.   I did not see any real solutions, just that it appears to be happening to multiple users hanging monitors off of laptops.  I'm guessing that you are cloning your desktop?

You may want to make your external monitor the 2nd monitor (extend the display but set it as primary) and see if that helps.  Maybe if the laptop monitor is the 2nd screen it will not cause the DX error.

It may help the dev team track it down w/o having to replicate themselves.

Yes, I am.  I normally run with the lid closed, using only the external monitor, which is probably why I hadn't noticed this before.