.ix slicing doesn't work on a dataframe obtained by groupby.get_group()
I have a dataframe with a column "actor"; I created a groupby object as such: 

a = df.groupby('actor')

Then I create a new DataFrame as follows: 

b = a.get_group(a.groups.keys()[0])

Now, b.ix[0,0] gives an error: 

KeyError: 0L

I can still use .ix to slice by index and column, but not by position.
