shift doesn't maintain timestamp datatype
So far so good...
pd.Series(pd.date_range("2000-1-1","2000-1-10"))
0   2000-01-01 00:00:00
1   2000-01-02 00:00:00
2   2000-01-03 00:00:00
3   2000-01-04 00:00:00
4   2000-01-05 00:00:00
5   2000-01-06 00:00:00
6   2000-01-07 00:00:00
7   2000-01-08 00:00:00
8   2000-01-09 00:00:00
9   2000-01-10 00:00:00

pd.Series(pd.date_range("2000-1-1","2000-1-10")).shift(1)

0             NaN
1    9.466848e+17
2    9.467712e+17
3    9.468576e+17
4    9.469440e+17
5    9.470304e+17
6    9.471168e+17
7    9.472032e+17
8    9.472896e+17
9    9.473760e+17
