BUG: DataFrame.(any|all) inconsistency

doc/source/whatsnew/v1.2.0.rst

@@ -419,6 +419,7 @@ Numeric
 ^^^^^^^
 - Bug in :func:`to_numeric` where float precision was incorrect (:issue:`31364`)
 - Bug in :meth:`DataFrame.any` with ``axis=1`` and ``bool_only=True`` ignoring the ``bool_only`` keyword (:issue:`32432`)
+- Bug in :meth:`DataFrame.any` and :meth:`DataFrame.all` with object-dtype columns sometimes returning larger :class:`Series` when operating on a subset of columns (:issue:`34918`)
 - Bug in :meth:`Series.equals` where a ``ValueError`` was raised when numpy arrays were compared to scalars (:issue:`35267`)
 - Bug in :class:`Series` where two :class:`Series` each have a :class:`DatetimeIndex` with different timezones having those indexes incorrectly changed when performing arithmetic operations (:issue:`33671`)
 - Bug in :meth:`pd._testing.assert_almost_equal` was incorrect for complex numeric types (:issue:`28235`)

pandas/core/internals/managers.py

@@ -27,6 +27,7 @@
 )
 from pandas.core.dtypes.common import (
     DT64NS_DTYPE,
+    is_bool_dtype,
     is_dtype_equal,
     is_extension_array_dtype,
     is_list_like,
@@ -713,8 +714,9 @@ def get_bool_data(self, copy: bool = False) -> "BlockManager":
         copy : bool, default False
             Whether to copy the blocks
         """
-        self._consolidate_inplace()
-        return self._combine([b for b in self.blocks if b.is_bool], copy)
+        # Note: use is_bool_dtype instead of blk.is_bool to exclude
+        #  object-dtype blocks containing all-bool entries.
+        return self._combine([b for b in self.blocks if is_bool_dtype(b.dtype)], copy)
 
     def get_numeric_data(self, copy: bool = False) -> "BlockManager":
         """

pandas/tests/internals/test_internals.py

@@ -687,6 +687,20 @@ def test_get_bool_data(self):
             np.array([True, False, True]),
         )
 
+    def test_get_bool_data_consistency(self):
+        # GH#34918
+        ser = Series([True, False, True], dtype=object)
+        ser2 = Series(["A", "B", "C"])
+        df = ser.to_frame("A")
+
+        expected = DataFrame(index=ser.index)
+        bd1 = df._get_bool_data()
+        tm.assert_frame_equal(bd1, expected)
+
+        df["B"] = ser2
+        bd2 = df._get_bool_data()
+        tm.assert_frame_equal(bd2, expected)
+
     def test_unicode_repr_doesnt_raise(self):
         repr(create_mgr("b,\u05d0: object"))