Hack to preserve behavior of #21309

Author: toobaz

pandas/core/frame.py

@@ -2663,6 +2663,10 @@ def _ixs(self, i, axis=0):
     def __getitem__(self, key):
         key = com._apply_if_callable(key, self)
 
+        # remove following two lines when a decision is taken on #21309:
+        if isinstance(self.columns, MultiIndex) and not self.columns.is_unique:
+            return self._getitem_multilevel(key)
+
         # shortcut if we are an actual column
         try:
             return self._getitem_column(key)