Date changes over night, not good

Hi All
I have a little problem where dates are changing overnight.
Using 8.1.2 on Redhat es4 64bit.
Not all records are affected.  Only records that have been recently updated
seem to suffer from this.  I originally thought it could be a problem with
auto vacuum, but that is off in the conf file.

Could auto vacuum be running anyway, could it be an earlier version.

Has anybody got any ideas to point me in the right direction.

Regards Chris
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