Basically put your computer thinks you're disconnecting the monitor. The same will happen if you plug another in.
Disabling that (which seems to be that feature Leo said) should fix it.
Another way would be to do what I do and run the game in a VM.
Googled and looked in my nVidia tool but nowhere to disable it, dont seem it is even able to be disabled unless switching to VGA. So i guess my old videocard didnt support HDCP lol
I'll try asking on Geforce forum, but seems like its a dead end,