Problem when setting values based on MultiIndex subset
```
from pandas import *
test = read_csv('/home/arthur/transform_issue.csv')
x =test.groupby(['A','B','C'])['revenues'].first().index
test.set_index(['A','B','C'], inplace=True)
test.ix[x]['revenues']= 999.99

print test.ix[x].shape
print test[test.revenues==999.99]

(127, 5)
Empty DataFrame
Columns: array([D, E, week, revenues, orders], dtype=object)
Index: array([], dtype=object)
```

I then tried setting via df[col][indexes] which simply crashed my session without any exception

```
test = read_csv('/home/arthur/transform_issue.csv')
x =test.groupby(['A','B','C'])['revenues'].first().index
test.set_index(['A','B','C'], inplace=True)
test['revenues'][x]= 999.99

print test.ix[x].shape
print test[test.revenues==999.99]
```

I sent the csv via email to wes@lambdafoundry.com
