Issue 1:
Code Sample, a copy-pastable example if possible

import io
import pandas
csv_file = io.StringIO("""datetime,cloudcover_eddh,dewpoint,dewpoint_eddh,humidity,humidity_eddh,lat,lon,precipitation_eddh,pressure_eddh,temperature,temperature_eddh,winddirection_eddh,windgust_eddh,windspeed_eddh
2016-01-01 00:00:00,CAVOC,4.1,3.0,100.0,94.0,53.5443,9.926839999999999,,1023.0,4.1,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,1.7,3.0,96.0,94.0,53.61297,9.98145,,1023.0,2.3,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,2.4,3.0,98.0,94.0,53.57735,10.09428,,1023.0,2.7,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,3.0,3.0,94.0,94.0,53.68849,10.1335,,1023.0,3.9,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,4.2,3.0,76.0,94.0,53.6608,10.06555,,1023.0,,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,3.0,3.0,100.0,94.0,53.43252,10.297989999999999,,1023.0,3.0,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,1.9,3.0,92.0,94.0,53.68937,10.13025,,1023.0,3.1,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,3.5,3.0,100.0,94.0,53.6344,9.966560000000001,,1023.0,3.5,3.0,160.0,0.0,7.2
2016-01-01 00:00:00,CAVOC,3.6,3.0,99.0,94.0,53.46402,9.89157,,1023.0,3.7,3.0,160.0,0.0,7.2""")
data_df = pandas.read_csv(csv_file, parse_dates=["datetime"], index_col="datetime")
cloud_cover_df = pandas.get_dummies(data_df.cloudcover_eddh, prefix="cloudcover_eddh")
df_hour = pandas.get_dummies(data_df.index.hour, prefix="hour")
data_df.reset_index(inplace=True, drop=True)
data_df = pandas.concat([
data_df,
df_hour,
cloud_cover_df
], axis=1, ignore_index=True)

Problem description

I expect that the three dataframes are concatenated as wished. I know that the indices correspond so I do not need pandas to check that for me. Instead I get the following error message:

File "<stdin>", line 5, in <module>
File "/informatik2/students/home/1kastner/.local/lib/python3.5/site-packages/pandas/core/reshape/concat.py", line 207, in concat
return op.get_result()
File "/informatik2/students/home/1kastner/.local/lib/python3.5/site-packages/pandas/core/reshape/concat.py", line 401, in get_result
indexers[ax] = obj_labels.reindex(new_labels)[1]
File "/informatik2/students/home/1kastner/.local/lib/python3.5/site-packages/pandas/core/indexes/base.py", line 2887, in reindex
indexer, missing = self.get_indexer_non_unique(target)
File "/informatik2/students/home/1kastner/.local/lib/python3.5/site-packages/pandas/core/indexes/base.py", line 2708, in get_indexer_non_unique
indexer, missing = self._engine.get_indexer_non_unique(tgt_values)
File "pandas/_libs/index.pyx", line 325, in pandas._libs.index.IndexEngine.get_indexer_non_unique (pandas/_libs/index.c:7722)
TypeError: 'NoneType' object is not iterable

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None

python: 3.5.2.final.0

python-bits: 64

OS: Linux

OS-release: 4.10.0-33-generic

machine: x86_64

processor: x86_64

byteorder: little

LC_ALL: None

LANG: en_US.UTF-8

LOCALE: en_US.UTF-8

pandas: 0.20.3

pytest: None

pip: 9.0.1

setuptools: 36.0.1

Cython: None

numpy: 1.13.1

scipy: 0.17.0

xarray: None

IPython: None

sphinx: None

patsy: None

dateutil: 2.6.1

pytz: 2017.2

blosc: None

bottleneck: None

tables: 3.2.2

numexpr: 2.6.2

feather: None

matplotlib: 1.5.1

openpyxl: None

xlrd: None

xlwt: None

xlsxwriter: 0.7.3

lxml: None

bs4: 4.4.1

html5lib: 0.999

sqlalchemy: None

pymysql: None

psycopg2: None

jinja2: 2.8

s3fs: None

pandas_gbq: None

pandas_datareader: None

Issue 2:
When concatting two dataframes where there are a) there are duplicate columns in one of the dataframes, and b) there are non-overlapping column names in both, then you get a IndexError:

In [9]: df1 = pd.DataFrame(np.random.randn(3,3), columns=['A', 'A', 'B1'])
...: df2 = pd.DataFrame(np.random.randn(3,3), columns=['A', 'A', 'B2'])

In [10]: pd.concat([df1, df2])

Traceback (most recent call last):
File "<ipython-input-10-f61a1ab4009e>", line 1, in <module>
pd.concat([df1, df2])
...
File "c:\users\vdbosscj\scipy\pandas-joris\pandas\core\index.py", line 765, in take
taken = self.view(np.ndarray).take(indexer)
IndexError: index 3 is out of bounds for axis 0 with size 3

I don't know if it should work (although I suppose it should, as with only the duplicate columns it does work), but at least the error message is not really helpfull.