RETRO-GAMING: ANNOUNCING BETA RELEASE OF RECALBOX FOR THE ROCKPRO64

[pimseb]

Ok I've been playing with screen resolution during the whole afternoon but it's still driving me nuts 
I've put the option HDMI-A-1:1280x1024@60 in extlinux.conf

I've made some screenshots to be clear.
When recalbox boots up, the screen is in the wanted 1280x1024 resolution (sorry image is not really good) :



The splash screen is cut surely because it's meant to be on full HD screens but it's not an issue for me.

Then comes the recalbox main menu which is, as you can see below, also in the correct resolution of 1280x1024 :



When I try to launch a game (mame, libretro, snes ...I tried almost all of them) the screen then turns into a 1280x720 resolution for a reason I don't understand :



I tried to change inside the libretro core by hitting the hotkey + X :

This is the core provided aspect ratio :



And this is when I try to change the custom aspect ratio settings. I can't get it into full screen, I always have parts of the screen that remain black (here on the right side) even when playing with the Ratio X position settings :



Well I'm not sure it's a RockPRo64 related problem but I'd like to be able to play the games full screen 
Thank you