fix(text area): end mouse selection only if currently selecting

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Fixed
+
+- Fixed `TextArea` to end mouse selection only if currently selecting https://github.com/Textualize/textual/pull/4436
+
 ## [0.57.1] - 2024-04-20
 
 ### Fixed

src/textual/widgets/_text_area.py

@@ -1513,17 +1513,18 @@ async def _on_mouse_move(self, event: events.MouseMove) -> 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()
+        if self._selecting:
+            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."""
+        """Finalize the selection that has been made using the mouse when the widget is hidden."""
         self._end_mouse_selection()
 
     async def _on_paste(self, event: events.Paste) -> None: