value_counts() is changing dates
Code:

``` python
    print fl['TurnOnDate'].head()
    print 'dtype:'
    print fl['TurnOnDate'].dtype
    print fl['TurnOnDate'].value_counts().head()
```

Result:

2723   2003-10-01 00:00:00
2841   2011-08-01 00:00:00
2855   2004-12-01 00:00:00
2941   2010-08-01 00:00:00
3019   2005-11-01 00:00:00
Name: TurnOnDate
dtype:
datetime64[ns]
1970-01-23 00:00:00    4
1970-01-19 00:00:00    4
1970-01-21 00:00:00    2
1970-01-22 00:00:00    2
1970-01-20 08:00:00    2
