Application's resolution not respected in fullscreen

[Anarky]

Hello, I wanted to benchmark optirun, primusrun and nvidia-xrun with Unigine Heaven.

On its launcher, if I select 1280x720 with fullscreen mode, the application is run with my screen resolution (1920x1080) as I can see on its settings. Even if I reselect 1280x720, the screen goes black for a few seconds, but 1920x1080 is still applied.

If it helps, the issue is the same if I launch it directly or with my windows manager (Awesome).
But with optirun or primusrun the benchmark stays at the desired resolution in fullscreen.