Setting the label parameter in the call to DF.plot alters the DataFrame's index name
Setting the label parameter in the call to df.plot alters the DataFrame's index name. For example,

```
df = pd.DataFrame(data=np.random.rand(5,3), index=np.arange(5), columns=['A', 'B', 'C'])
df.index.name='RowNumber'
df.plot(y='B', label='Test')
print df.index.name

Out[1]: Test
```

See a better example at [StackOverflow](http://stackoverflow.com/questions/26068598/specifying-y-array-and-plot-label-in-pandas-dataframe-plot-changes-the-dataframe). 
[An answer in above link](http://stackoverflow.com/questions/26068598/specifying-y-array-and-plot-label-in-pandas-dataframe-plot-changes-the-dataframe/26070511#26070511) points problem to [here](https://github.com/pydata/pandas/blob/master/pandas/tools/plotting.py#L2278). 
pandas version 0.14.1. 
