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That tweak doesnt actually work, i have a sim free model and ive done all the tweaks related to that part ie the screen turning off whilst on a call and it doesnt work.
Not such a big problem as i just press the power button and the screen comes back on. Reason why it turns off is so that you dont accidentally press any of the on screen buttons with your face etc and its happened to me a few times.
It didn't work for me the first time i changed the setting but I tried it again at the same time as altering another few settings and now it works fine.
I think it was face-down mute, phone-sleep during call and fast-sleep during call that I changed.