Launching demul from Bigbox does not allow fullscreen mode

[Former user]

Repro steps

Setup demul, ensure start in fullscreen is checked. Run Demul via windows without BigBox - game runs in full screen Run Launchbox, launch game - game runs in full screen Run Bigbox, launch game - game only runs in windowed mode (smallest)

[Lord Monkus]

Demul launches in fullscreen mode just fine.