Stacking MultiIndex DataFrame columns with Timestamps levels fails
You can see the bug in the following code:

```
import pandas as pd
import datetime as dt

key = pd.MultiIndex.from_tuples([(
                            dt.datetime(2014,8,1,0,0,0),
                            'SomeColumnName',
                            'AnotherOne')])

data = {
    '1' : 34204,
    '2' : 43580,
    '3' : 84329,
    '5' : 23485
}


ts = pd.Series(data=data)
df = pd.DataFrame(data=ts, columns=key)

stacked = df.stack()

print stacked
```

We would expect the data to be unchanged, however the returned DataFrame is empty. 

The Pandas version used was 0.11.0
