Series.pop() removes additional keys not specified
``` python
import pandas as pd
df = pd.DataFrame({
    'A': 0, 
    'B': range(5), 
    'C': 0, 
    })
k = df.iloc[4]
k.pop('B')
print k
```

```
out:
A    0
Name: 4, dtype: int64
```

```
expected:
A    0
C    0
Name: 4, dtype: int64

```

```
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.4.final.0
python-bits: 64
OS: Linux
OS-release: 3.8.0-33-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: de_DE.UTF-8

pandas: 0.13.1
Cython: 0.17.4
numpy: 1.7.1
scipy: 0.11.0
statsmodels: 0.5.0
IPython: 0.13.2
sphinx: 1.1.3
patsy: 0.2.1
scikits.timeseries: None
dateutil: 1.5
pytz: 2012c
bottleneck: None
tables: 2.4.0
numexpr: 2.0.1
matplotlib: 1.2.1
openpyxl: 1.7.0
xlrd: 0.6.1
xlwt: 0.7.4
xlsxwriter: None
sqlalchemy: None
lxml: None
bs4: None
html5lib: None
bq: None
apiclient: None
```
