The Date of my Macbook pro 2012 changes periodically at Dec 5th 2013

Hello all,

The date of my Macbook Pro 2012 changes periodically at Dec 5th 2013 23:00

It happens when it's on or when it wakes up

I reset PRAM and SMC but have seen no change

When I open the date settings, the automatic update which is on puts the right date instantly

What can cause this problem ? I've not found anything on the internet of someone having the same problem