Starting in 2023.2 and going forward, Pointer events and their corresponding Mouse events are propagated at the same time. This simplifies the workflow and helps migrating from mouse to pointer events, which are more flexible and the recommended way to handle all pointer types.

A consequence of this simplification is that the MouseDownEvent is now received by its target *before* the focus is modified. When the MouseDownEvent callback calls Focus() on an element, that focus is very quickly replaced by the target of the MouseDownEvent. This behavior is exactly matching the behavior of the PointerDownEvent in 2022.3 and earlier, which is what Unity is aiming for.

This problem can be fixed by adding
{code:c#}rootVisualElement.focusController.IgnoreEvent(e);{code} to the MouseDownEvent callback method after e.StopPropagation():

{code:c#}
private void OnMouseDownEvent(PointerDownEvent e) {
if (e.clickCount != 2)
return;
FocusTitleEditor();
e.StopPropagation();
rootVisualElement.focusController.IgnoreEvent(e);
}
{code}