BUG: DataFrame._item_cache not cleared on on .copy()

doc/source/whatsnew/v1.1.0.rst

@@ -363,6 +363,7 @@ Indexing
 - Bug in :class:`Index` constructor where an unhelpful error message was raised for ``numpy`` scalars (:issue:`33017`)
 - Bug in :meth:`DataFrame.lookup` incorrectly raising an ``AttributeError`` when ``frame.index`` or ``frame.columns`` is not unique; this will now raise a ``ValueError`` with a helpful error message (:issue:`33041`)
 - Bug in :meth:`DataFrame.iloc.__setitem__` creating a new array instead of overwriting ``Categorical`` values in-place (:issue:`32831`)
+- Bug in :meth:`DataFrame.copy` _item_cache invalidated after copy performs consolidation (:issue:`31784`)
 
 Missing
 ^^^^^^^

pandas/core/generic.py

@@ -5680,6 +5680,7 @@ def copy(self: FrameOrSeries, deep: bool_t = True) -> FrameOrSeries:
         dtype: object
         """
         data = self._data.copy(deep=deep)
+        self._clear_item_cache()
         return self._constructor(data).__finalize__(self)
 
     def __copy__(self: FrameOrSeries, deep: bool_t = True) -> FrameOrSeries:

pandas/tests/generic/test_generic.py

@@ -910,3 +910,21 @@ def test_axis_classmethods(self, box):
             assert obj._get_axis_number(v) == box._get_axis_number(v)
             assert obj._get_axis_name(v) == box._get_axis_name(v)
             assert obj._get_block_manager_axis(v) == box._get_block_manager_axis(v)
+
+    def test_cache_on_copy(self):
+        df = DataFrame({"a": [1]})
+
+        df["x"] = [0]
+        df["a"]
+
+        df.copy()
+
+        df["a"].values[0] = -1
+
+        assert df["a"].values[0] == -1
+        tm.assert_frame_equal(df, DataFrame({"a": [-1], "x": [0]}))
+
+        df["y"] = 0
+
+        assert df["a"].values[0] == -1
+        tm.assert_frame_equal(df, DataFrame({"a": [-1], "x": [0], "y": [0]}))