BUG: add back check for MultiIndex case and take_split_path

pandas/core/indexing.py

@@ -321,6 +321,19 @@ def _setitem_with_indexer(self, indexer, value):
                 val = list(value.values()) if isinstance(value, dict) else value
                 take_split_path = not blk._can_hold_element(val)
 
+        if isinstance(indexer, tuple) and len(indexer) == len(self.obj.axes):
+
+            for i, ax in zip(indexer, self.obj.axes):
+
+                # if we have any multi-indexes that have non-trivial slices
+                # (not null slices) then we must take the split path, xref
+                # GH 10360
+                if isinstance(ax, MultiIndex) and not (
+                    is_integer(i) or com.is_null_slice(i)
+                ):
+                    take_split_path = True
+                    break
+
         if isinstance(indexer, tuple):
             nindexer = []
             for i, idx in enumerate(indexer):

pandas/tests/indexing/multiindex/test_loc.py

@@ -390,3 +390,15 @@ def test_loc_getitem_lowerdim_corner(multiindex_dataframe_random_data):
     expected = 0
     result = df.sort_index().loc[("bar", "three"), "B"]
     assert result == expected
+
+
+def test_loc_setitem_object_array():
+    # case from https://github.com/pandas-dev/pandas/issues/27841
+    df = DataFrame(
+        "string",
+        index=list("abcd"),
+        columns=MultiIndex.from_product([["Main"], ("another", "one")]),
+    )
+    df["labels"] = "a"
+    df.loc[:, "labels"] = df.index
+    tm.assert_numpy_array_equal(np.asarray(df["labels"]), np.asarray(df.index))