mi4 lte exposure problem

Hi. I just have bought a new mi4 lte cu. But the problem is the exposure time is very buggy. When i choose 1/2s or 1/4s, it will take a photo with 2s exposure time. I used the 32s exposure patch but >2s dont work. It take picture as fast as 2s exposure time. I heard that some mi4 go with samsung sensor instead of sony imx214. How can i fix my problem? Please help me

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