Ensure that the mouse is released when a TextArea gets hidden

Fixes Textualize#4292.

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed `OptionList.OptionHighlighted` leaking out of `Select` https://github.com/Textualize/textual/issues/4224
 - Fixed `Tab` enable/disable messages leaking into `TabbedContent` https://github.com/Textualize/textual/issues/4233
 - Fixed a style leak from `TabbedContent` https://github.com/Textualize/textual/issues/4232
+- Fixed the mouse not being released when hiding a `TextArea` while mouse selection is happening https://github.com/Textualize/textual/issues/4292
 
 ### Changed
 

src/textual/widgets/_text_area.py

@@ -1498,13 +1498,21 @@ async def _on_mouse_move(self, event: events.MouseMove) -> None:
             selection_start, _ = self.selection
             self.selection = Selection(selection_start, target)
 
-    async def _on_mouse_up(self, event: events.MouseUp) -> None:
+    def _end_mouse_selection(self) -> None:
         """Finalize the selection that has been made using the mouse."""
         self._selecting = False
         self.release_mouse()
         self.record_cursor_width()
         self._restart_blink()
 
+    async def _on_mouse_up(self, event: events.MouseUp) -> None:
+        """Finalize the selection that has been made using the mouse."""
+        self._end_mouse_selection()
+
+    async def _on_hide(self, event: events.Hide) -> None:
+        """Finalize the selection that has been made using the mouse when thew widget is hidden."""
+        self._end_mouse_selection()
+
     async def _on_paste(self, event: events.Paste) -> None:
         """When a paste occurs, insert the text from the paste event into the document."""
         if self.read_only: