Thanks a million for documenting this. Helped me finally succeed after a good 20 mins of trying to work this out. In doing so, I also found a workaround for your purgatory issue…
- Click and drag the subtask from the parent task into whatever section you want it to become a task in. (When you’ve done this, it appears both in the section and as a subtask under the original parent task.)
- Click and drag the subtask from the parent task a second time. This time, drop it over in the left-hand panel you mentioned – into the project itself.
Now, instead of it being landing in purgatory, it appears as a task of its own in the section you dragged it into in step 1. It is also removed from the parent task.