"cannot reindex from a duplicate axis" when groupby().apply() on MultiIndex columns
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
import numpy as np

df = pd.DataFrame(
    np.ones([6, 4], dtype=int),
    columns=pd.MultiIndex.from_product([['A', 'B'], [1, 2]])
)

(
    df
    .groupby(level=0, axis=1)
    .apply(
        lambda df: pd.concat(
            [df.xs(df.name, axis=1), df.sum(axis=1).to_frame('Total')], 
            axis=1
        )
    )
)

```
#### Problem description

The code above produces the error:

> cannot reindex from a duplicate axis

I believe this is a bug because, as described below, essentially the same operations can be successfully run along the other axis.

#### Expected Output

It should, as far as I can tell, produce the following output:

![image](https://user-images.githubusercontent.com/15697539/26962477-b92ed344-4d29-11e7-9cd8-ca5406eee097.png)

The desired output can be obtained when working on the transposed DataFrame along the `index` rather than the `columns`:

```python
(
    df
    .T
    .groupby(level=0)
    .apply(
        lambda df: pd.concat(
            [df.xs(df.name), df.sum().to_frame('Total').T]
        )
    )
    .T
)
```

#### Output of ``pd.show_versions()``

<details>

pd.show_versions()
pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.9.final.0
python-bits: 64
OS: Windows
OS-release: 8
machine: AMD64
processor: Intel64 Family 6 Model 69 Stepping 1, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.20.2
pytest: None
pip: 9.0.1
setuptools: 34.3.3
Cython: None
numpy: 1.13.0
scipy: 0.19.0
xarray: None
IPython: 5.3.0
sphinx: None
patsy: None
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.0.0
openpyxl: None
xlrd: 1.0.0
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.999
sqlalchemy: None
pymysql: None
psycopg2: 2.7.1 (dt dec pq3 ext lo64)
jinja2: 2.9.5
s3fs: None
pandas_gbq: None
pandas_datareader: None

</details>
