How Do I Get My 360 To Go Back To 50Hz?

I know this is supposed to be obvious, but I've been at it for about an hour now as my console refuses to go back to 50Hz. I have a Full HDTV and run my 360 by HDMI, previously I ran it at 1080p 50Hz, but now it is running at 1080p 60Hz which is causing some jittering to some of my games that run at 24fps.

I've gone into settings and anytime it asks me to keep the setting at 50hz, which is displayed correctly I say yes, only it doesn't change my TV still says its still running at 60Hz. My TV is PAL so its default is 50Hz, its a Panasonic Viera Plasma if that helps anyone.

Also I don't get any jittering with games on other TVs or games that run at 25fps.

Nearly every tv nowadays runs at 60hz bare minimum because that is the refresh rate of every game and television broadcast, the increase of hz on tvs now is a way to cheat it to be higher, thats why games have a bit more lag when you crank the hz up to 120, 240 etc. you cant get your 360 to run at 50hz because the hardware wont allow it on newer tvs, plug it in to an old crt tv and it will run at 50.

how and why are u making games run at 24fps? using the 24p mode? if so thats meant to be for movies...because they were shot at 24 FPS. games on the other hand try and run at as many fps as they can or have frame caps (bioshock, halo, etc)