Unexpected shift() and tshift() behavior with StaticTzInfo datetimes

[joshpurvis]

When shifting a DateTimeIndex with a StaticTzInfo (namely EST in my case), I'm seeing odd behavior in which it first seems to be shifting -5 (the offset for EST), and then shifting relative to that:

import pandas as pd
import pytz
import datetime

dt = datetime.datetime(2014, 11, 14, 0)
dt_est = pytz.timezone('EST').localize(dt)
s = pd.Series(data=[1], index=[dt_est])

s.shift(0, freq='h')  # 2014-11-14 00:00:00-05:00 (seems okay) 
s.shift(-1, freq='h')  # 2014-11-13 18:00:00-05:00 (expected 2014-11-13 23:00:00)
s.shift(1, freq='h')  # 2014-11-13 20:00:00-05:00 (expected 2014-11-14 01:00:00)

s.shift(-1, freq='s')  # 2014-11-13 18:59:59-05:00 (same with other freq)

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Linux
OS-release: 3.13.0-39-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.15.0
nose: 1.3.4
Cython: 0.21.1
numpy: 1.9.0
scipy: 0.14.0
statsmodels: None
IPython: 2.3.0
sphinx: None
patsy: 0.3.0
dateutil: 2.2
pytz: 2014.4
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.4.0
openpyxl: 1.8.6
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
rpy2: None
sqlalchemy: None
pymysql: None
psycopg2: None

[jreback]

thanks this is a dupe of #8616

pull-requests to fix are welcome of course!

[jreback]

@joshpurvis I have marked it their as well, the underlying cause is that issue.