bug: double print statement in groupby / apply
#### Code Sample

This is based on http://stackoverflow.com/questions/39268147/understand-pandas-groupby-apply-behaviour/39268538#39268538. 

```
import seaborn as sns
iris = sns.load_dataset('iris')
iris.ix[1:100:10].groupby(["species"]).apply(lambda x: print(len(x), '\n***\n', x))            ## first try
iris.ix[1:100:10].groupby(["species"]).apply(lambda x: print(len(x), x.name, '\n***\n', x)) ## second try
```
#### Expected Output

The first line prints one of the groups doubled, which is unexpected. The second line doesn't double. 
#### output of `pd.show_versions()`

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-34-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.2
setuptools: 23.0.0
Cython: 0.24
numpy: 1.10.4
scipy: 0.17.1
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: 1.4.1
patsy: 0.4.1
dateutil: 2.2
pytz: 2016.4
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.5.2
matplotlib: 1.5.1
openpyxl: 2.2.0-b1
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.2
lxml: 3.6.0
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.13
pymysql: None
psycopg2: 2.6.1 (dt dec pq3 ext)
jinja2: 2.8
boto: 2.40.0
pandas_datareader: None
```
