Odd behaviour in read_csv
This is a strange example from [this StackOverflow question](http://stackoverflow.com/questions/14237749/pandas-read-csv-strange-behavior-for-empty-default-values):

```
Date,Currenncy,Symbol,Type,Units,UnitPrice,Cost,Tax
2012-03-14,USD,AAPL,BUY,1000
2012-05-12,USD,SBUX,SELL,500
```

```
In [1]: pd.read_csv('ttt.csv', index_col=0, parse_dates=True)
Out[1]: 
           Currenncy Symbol  Type  Units   UnitPrice       Cost       Tax
Date                                                                     
2012-03-14       USD   AAPL   BUY   1000  2012-05-12  012-05-12  12-05-12
2012-02-05       USD   SBUX  SELL    500         NaN        NaN       NaN
```
