Help, can't update RTC of my Mi2S so it went back to 1970 after every shutdown.

EDIT: I'm temporary using a workaround and it works pretty fine, and I think it will continue work as long as my RTC clock keeps running...
http://forum.xda-developers.com/showthread.php?p=52451847

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Recently I've noticed that my Mi2S can't remember the time goes back to 1970 after shutdown (even if I don't pull the battery)

I installed busybox and used hwclock -r, shows:
Sun Jan 4 15:25:49 1970 0.000000 seconds

And use date to check my local time (updated via network)...

Help, can't update RTC of my Mi2S so it went back to 1970 after every shutdown.