Thanks for the explanation - I may not have expressed my request well:
I am not proposing a behavior change, but a shortcut of sorts (using a modifier key) for the following sequence:
1. Drag and drop a task onto a collapsed parent task (which expands that task and scrolls down to the dropped task at the end of the list of subtasks)
2. Scroll back up to the dropped task's new parent task.
3. Click the new parent task's [-], which collapses and selects the new parent task.
I find myself often sorting task into long lists (categories) of subtasks, which results in a lot of manual scrolling (see the linked GIF below).