Fix for issue pandas-dev#28283: Ensure __finalize__ propagates metada…

…ta correctly

pandas/core/generic.py

@@ -5972,27 +5972,32 @@ def pipe(
     # Attribute access
 
     @final
-    def __finalize__(self, other, method: str | None = None, **kwargs) -> Self:
-        """
-        Propagate metadata from other to self.
 
-        Parameters
-        ----------
-        other : the object from which to get the attributes that we are going
-            to propagate
-        method : str, optional
-            A passed method name providing context on where ``__finalize__``
-            was called.
+@final
+def __finalize__(self, other, method: str | None = None, **kwargs) -> Self:
+    """
+    Propagate metadata from other to self.
+
+    Parameters
+    ----------
+    other : the object from which to get the attributes that we are going
+        to propagate
+    method : str, optional
+        A passed method name providing context on where ``__finalize__``
+        was called.
 
-            .. warning::
+        .. warning::
+
+           The value passed as `method` are not currently considered
+           stable across pandas releases.
+    """
+    if isinstance(other, NDFrame):
+        if other.attrs:
+            self.attrs.update(other.attrs)
+        if hasattr(other, 'flags'):
+            self.flags = other.flags
+    return self
 
-               The value passed as `method` are not currently considered
-               stable across pandas releases.
-        """
-        if isinstance(other, NDFrame):
-            if other.attrs:
-                # We want attrs propagation to have minimal performance
-                # impact if attrs are not used; i.e. attrs is an empty dict.
                 # One could make the deepcopy unconditionally, but a deepcopy
                 # of an empty dict is 50x more expensive than the empty check.
                 self.attrs = deepcopy(other.attrs)