I noticed that when I have a shared list, creating a child task under a closed task will reopen the parent task & even update its timestamp, but it will not update the name of the user who last updated the parent task.
So if I there is a task 1, which was closed yesterday by user A, and a task 2 is created by user B as a child of task 1, it will reopen task 1 and even update its timestamp to today, but task 1 will still show up as having been last updated by user A instead of user B.
This remains the case even if task 2 is then deleted: task 1 remains open with the updated timestamp but it still shows up as having been last updated by user A.