TST: a weird bug with numpy + DataFrame with duplicate columns (#38354)

Author: arw2019

pandas/tests/frame/test_nonunique_indexes.py

@@ -486,3 +486,36 @@ def test_set_value_by_index(self):
 
         df.iloc[:, 0] = 3
         tm.assert_series_equal(df.iloc[:, 1], expected)
+
+    @pytest.mark.parametrize(
+        "data1,data2,expected_data",
+        (
+            (
+                [[1, 2], [3, 4]],
+                [[0.5, 6], [7, 8]],
+                [[np.nan, 3.0], [np.nan, 4.0], [np.nan, 7.0], [6.0, 8.0]],
+            ),
+            (
+                [[1, 2], [3, 4]],
+                [[5, 6], [7, 8]],
+                [[np.nan, 3.0], [np.nan, 4.0], [5, 7], [6, 8]],
+            ),
+        ),
+    )
+    def test_masking_duplicate_columns_mixed_dtypes(
+        self,
+        data1,
+        data2,
+        expected_data,
+    ):
+        # GH31954
+
+        df1 = DataFrame(np.array(data1))
+        df2 = DataFrame(np.array(data2))
+        df = pd.concat([df1, df2], axis=1)
+
+        result = df[df > 2]
+        expected = DataFrame(
+            {i: np.array(col) for i, col in enumerate(expected_data)}
+        ).rename(columns={2: 0, 3: 1})
+        tm.assert_frame_equal(result, expected)