External screen "mirror" mode problem

[extracampine]

I am using an external screen (Sony HW40ES projector) connected to a USB port on my laptop. Running Windows 10, HS & Rocketlauncher. Use mirror mode so that I can use the big screen to play games. Seems to work fine.

Problem is, it doesn't work for some particular emulators - for example, the NES emulator (which in my setup uses Retroarch with the Nestopia core). When I load an NES game via HS, the loading screen appears on both screens fine, but then the external screen goes blank and the game only appears on the laptop screen - with the external screen then returning to the HS menu. When I exit the game, both screens return to the HS menu again.

Any help here would be much appreciated! No idea why Windows appears to be selective in it's mirroring function when it is supposed to mirror everything that is on the screen. It's like something is interfering with the mirroring function somewhere.