In Progress Can't lock screen on miui 3.1.11 SGS2

Jan 24, 2013
I can't lock my screen. I can put it to sleep/black but it will go on in my pocket and call random people. When i go to settings/security&privacy/screen security. When i turn on "power button instantly locks" and leave the setup menu it will go back to being off. Is there anything i can do to make it stay on? I already have made pattern but when i push the power button itll send me straight to the menu.

Miui version: 3.1.11
Phone: samsung galaxy s 2

Thanks in advance!