Logical comparison operators and mathematical operators are applied inconsistently for series.

[RobertasA]

In series all logical operators are by position (iloc) while all mathematical operators are by location (loc).
This is probably similar to #4581.

e.g.
import pandas as pd
a = pd.Series([1, 4], index=[0, 1])
b = pd.Series([3, 7], index=[1, 0])

a>b

Gives

0 False
1 False
dtype: bool

But

a - b

gives

0 -6
1 1
dtype: int64

output of pd.show_versions()

`

pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 2.7.10.final.0
python-bits: 64
OS: Darwin
OS-release: 15.5.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8

pandas: 0.18.1
nose: None
pip: 1.5.6
setuptools: 3.6
Cython: None
numpy: 1.11.1
scipy: None
statsmodels: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.5.3
pytz: 2016.4
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
boto: None
pandas_datareader: None
`

[jreback]

the description by @sinhrks on #1134 is complete description of this issue.