Tasks with subtasks from Tasks on Android get flattened on sync to mailbox.org via CalDAV
1. Set up DAVx5 sync of mailbox.org using CalDAV on Android
2. Create a task with a subtask
3. Sync via DAVx5
4. Inspect the task list in mailbox.org
Subtasks are kept.
Subtasks are on the same level as the original main task.