DataFrame.sum() inconsistent behavior treating full row/col of NANs
Seeing an odd issue. When doing a sum and the full column or row is NAN, I expect NAN as the result. Recently my system has been giving a sum of zero if the full row is NAN, unless skipna=FALSE is specified (but of course that screws up rows with only one NAN, for example). 

I would have thought skipna=TRUE, which is default, should give NAN if the full row is NAN per the docs.

This seems to be dependant on some combination of package versions but I cannot figure out why. I reinstalled completely to a fresh Anaconda 2.3.0 amd64 and the behaviour is the same.

See screenshot. For In[6] I expect index [0] to be NAN, not zero.

![image](https://cloud.githubusercontent.com/assets/13731237/9171885/4566e4e8-3f3d-11e5-8364-fdaefbc8a054.png)

My package list, for reference:

_license                  1.1                      py27_0  
alabaster                 0.7.3                    py27_0  
anaconda                  2.3.0                np19py27_0  
argcomplete               0.8.9                    py27_0  
astropy                   1.0.3                np19py27_0  
babel                     1.3                      py27_0  
backports.ssl-match-hostname 3.4.0.2                   <pip>
bcolz                     0.9.0                np19py27_0  
bdateutil                 0.1                       <pip>
beautiful-soup            4.3.2                    py27_1  
beautifulsoup4            4.3.2                     <pip>
binstar                   0.11.0                   py27_0  
bitarray                  0.8.1                    py27_1  
blaze                     0.8.0                     <pip>
blaze-core                0.8.0                np19py27_0  
blpapi                    3.5.3                     <pip>
blz                       0.6.2                np19py27_1  
bokeh                     0.9.0                np19py27_0  
boto                      2.38.0                   py27_0  
bottleneck                1.0.0                np19py27_0  
cdecimal                  2.3                      py27_1  
certifi                   14.05.14                 py27_0  
cffi                      1.1.0                    py27_0  
clyent                    0.3.4                    py27_0  
colorama                  0.3.3                    py27_0  
conda                     3.15.1                   py27_0  
conda-build               1.14.1                   py27_0  
conda-env                 2.3.0                    py27_0  
configobj                 5.0.6                    py27_0  
cryptography              0.9.1                    py27_0  
cvxopt                    1.1.7                     <pip>
cython                    0.22.1                   py27_0  
cytoolz                   0.7.3                    py27_0  
datashape                 0.4.5                np19py27_0  
dateutil                  2.4.1                    py27_0  
decorator                 3.4.2                    py27_0  
docutils                  0.12                     py27_1  
dynd-python               0.6.5                np19py27_0  
enum34                    1.0.4                    py27_0  
fastcache                 1.0.2                    py27_0  
flask                     0.10.1                   py27_1  
funcsigs                  0.4                      py27_0  
gevent                    1.0.1                    py27_0  
gevent-websocket          0.9.3                    py27_0  
greenlet                  0.4.7                    py27_0  
grin                      1.2.1                    py27_2  
h5py                      2.5.0                np19py27_1  
hdf5                      1.8.15.1                      2  
holidays                  0.3.1                     <pip>
idna                      2.0                      py27_0  
ipaddress                 1.0.7                    py27_0  
ipython                   3.2.0                    py27_0  
ipython-notebook          3.2.0                    py27_0  
ipython-qtconsole         3.2.0                    py27_0  
itsdangerous              0.24                     py27_0  
jdcal                     1.0                      py27_0  
jedi                      0.8.1                    py27_0  
jinja2                    2.7.3                    py27_2  
jsonschema                2.4.0                    py27_0  
launcher                  1.0.0                         1  
llvmlite                  0.5.0                    py27_0  
lxml                      3.4.4                    py27_0  
lz4                       0.7.0                     <pip>
markupsafe                0.23                     py27_0  
matplotlib                1.4.3                np19py27_1  
menuinst                  1.0.4                    py27_0  
mistune                   0.5.1                    py27_1  
mock                      1.0.1                    py27_0  
multipledispatch          0.4.7                    py27_0  
networkx                  1.9.1                    py27_0  
nltk                      3.0.3                np19py27_0  
node-webkit               0.10.1                        0  
nose                      1.3.7                    py27_0  
numba                     0.19.1               np19py27_0  
numexpr                   2.4.3                np19py27_0  
numpy                     1.9.2                    py27_0  
odo                       0.3.2                np19py27_0  
openpyxl                  1.8.5                    py27_0  
pandas                    0.14.1               np19py27_0  
patsy                     0.3.0                np19py27_0  
pep8                      1.6.2                    py27_0  
pillow                    2.8.2                    py27_0  
pip                       7.1.0                    py27_0  
ply                       3.6                      py27_0  
psutil                    2.2.1                    py27_0  
py                        1.4.27                   py27_0  
pyasn1                    0.1.7                    py27_0  
pycosat                   0.6.1                    py27_0  
pycparser                 2.14                     py27_0  
pycrypto                  2.6.1                    py27_3  
pyflakes                  0.9.2                    py27_0  
pygments                  2.0.2                    py27_0  
pymongo                   2.8                      py27_0  
pyodbc                    3.0.7                    py27_0  
pyopenssl                 0.15.1                   py27_1  
pyparsing                 2.0.3                    py27_0  
pyqt                      4.10.4                   py27_1  
pyreadline                2.0                      py27_0  
pytables                  3.2.0                np19py27_0  
pytest                    2.7.1                    py27_0  
python                    2.7.10                        0  
python-dateutil           2.4.2                    py27_0  
pytz                      2015.4                   py27_0  
pywin32                   219                      py27_0  
pyyaml                    3.11                     py27_1  
pyzmq                     14.7.0                   py27_0  
requests                  2.7.0                    py27_0  
rope                      0.9.4                    py27_1  
runipy                    0.1.3                    py27_0  
scikit-image              0.11.3               np19py27_0  
scikit-learn              0.16.1               np19py27_0  
scipy                     0.16.0               np19py27_0  
setuptools                18.0.1                   py27_0  
six                       1.9.0                    py27_0  
snowballstemmer           1.2.0                    py27_0  
sockjs-tornado            1.0.1                    py27_0  
sphinx                    1.3.1                    py27_0  
sphinx-rtd-theme          0.1.7                     <pip>
sphinx_rtd_theme          0.1.7                    py27_0  
spyder                    2.3.5.2                  py27_0  
spyder-app                2.3.5.2                  py27_0  
sqlalchemy                1.0.5                    py27_0  
ssl_match_hostname        3.4.0.2                  py27_0  
statsmodels               0.6.1                np19py27_0  
sympy                     0.7.6                    py27_0  
tables                    3.2.0                     <pip>
toolz                     0.7.2                    py27_0  
tornado                   4.2                      py27_0  
ujson                     1.33                     py27_0  
unicodecsv                0.9.4                    py27_0  
werkzeug                  0.10.4                   py27_0  
xlrd                      0.9.3                    py27_0  
xlsxwriter                0.7.3                    py27_0  
xlwings                   0.3.5                    py27_0  
xlwt                      1.0.0                    py27_0  
zlib                      1.2.8                         0  
