BUG: multiindex slice 1.1.0rc0
mulitindex slicing returns different (from pandas<=1.0.x) results in pandas 1.1.0rc0

```
df = pd.DataFrame( data=[[0,1,'a',1],[1,0,'a',0],[1,1,'b',1],[1,1,'c',2]], columns=['index','date','author','price'] )

# to keep the most recent date for every index (could happen in practice)
idx = df.drop_duplicates('index',keep='last').set_index(['index','date']).index 

df.set_index(['index','date']).loc[idx,:].reset_index()
```

df

 index | date  | author | price
-- | -- | -- | --
0|1|a | 1
1|0|a | 0
1|1|b | 1
1|1|c | 2






Result

  | | author | price
 -- | -- | --
(0, 1) | a | 1
(1, 1) | b | 1
(1, 1) | c | 2
