Thanks for the info Floatingyeti. I hadn't updated the mame core yet so I have been able to save it under the version name and change it in the rocketlauncher settings..
I also use different versions of Retroarch in order to "freeze" certain systems in their working state (hopefully).
Have you been able to pinpoint the problem in the retroarch module and/or determine what change caused the problem in the updated mame core ?