TST: Regression test for #33765

pandas/tests/frame/test_arithmetic.py

@@ -12,6 +12,7 @@
 import pandas as pd
 from pandas import (
     DataFrame,
+    Index,
     MultiIndex,
     Series,
 )
@@ -1782,3 +1783,22 @@ def test_inplace_arithmetic_series_update():
 
     expected = DataFrame({"A": [2, 3, 4]})
     tm.assert_frame_equal(df, expected)
+
+
+def test_arithemetic_multiindex_align():  # Needs a better name
+    """
+    Regression test for: https://github.com/pandas-dev/pandas/issues/33765
+    """
+    df1 = DataFrame(
+        [[1]],
+        index=["a"],
+        columns=MultiIndex.from_product([[0], [1]], names=["a", "b"]),
+    )
+    df2 = DataFrame([[1]], index=["a"], columns=Index([0], name="a"))
+    expected = DataFrame(
+        [[0]],
+        index=["a"],
+        columns=MultiIndex.from_product([[0], [1]], names=["a", "b"]),
+    )
+    result = df1 - df2
+    tm.assert_frame_equal(result, expected)