I have problem merging several time series to a common DataFrame. The example code I'm using:

import pandas
import datetime
import numpy as np

start = datetime.datetime(2001, 1, 1)
end = datetime.datetime(2001, 1, 10)
dates = pandas.date_range(start, end)
serie_1 = pandas.Series(np.random.randn(10), index = dates)
start = datetime.datetime(2001, 1, 2)
end = datetime.datetime(2001, 1, 11)
dates = pandas.date_range(start, end)
serie_2 = pandas.Series(np.random.randn(10), index = dates)
start = datetime.datetime(2001, 1, 3)
end = datetime.datetime(2001, 1, 12)
dates = pandas.date_range(start, end)
serie_3 = pandas.Series(np.random.randn(10), index = dates)

print 'serie_1'
print serie_1
print 'serie_2'
print serie_2
print 'serie_3'
print serie_3

serie_4 = pandas.concat([serie_1,serie_2], join='outer', axis = 1)
print 'serie_4'
print serie_4
serie_5 = pandas.concat([serie_4, serie_3], join='outer', axis = 1)
print 'serie_5'
print serie_5

This gives me the error for serie_5 (the second concat): 

Traceback (most recent call last):
  File "C:\Users\User\Workspaces\Python\Source\TestingPandas.py", line 29, in <module>
    serie_5 = pandas.concat([serie_4, serie_3], join='outer', axis = 1)
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 878, in concat
    verify_integrity=verify_integrity)
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 948, in __init__
    self.new_axes = self._get_new_axes()
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1101, in _get_new_axes
    new_axes[i] = self._get_comb_axis(i)
  File "C:\Python27\lib\site-packages\pandas\tools\merge.py", line 1125, in _get_comb_axis
    all_indexes = [x._data.axes[i] for x in self.objs]
AttributeError: 'TimeSeries' object has no attribute '_data'

I would like the result to look something like this (with random values in column 2):

                 0         1
python pandas time-series
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