diff --git a/src/textual/driver.py b/src/textual/driver.py
index 0e8ac6412c..3aee951efe 100644
--- a/src/textual/driver.py
+++ b/src/textual/driver.py
@@ -55,6 +55,7 @@ def process_event(self, event: events.Event) -> None:
                 and not event.button
                 and self._last_move_event is not None
             ):
+                # Deduplicate self._down_buttons while preserving order.
                 buttons = list(dict.fromkeys(self._down_buttons).keys())
                 self._down_buttons.clear()
                 move_event = self._last_move_event