User has two task lists "Aufgaben" and "Aufgabe2". Focus is on filter "Alle".
Both task list are empty and visible.
User creates two new Tasks "A1" and "A2" on task list "Aufgabe2".
User moves task "A1" to task "A2" via drag&drop. "A1" will be displayed correctly as a subtask of "A2".
User hides task list "Aufgaben" before the page is refreshed.
Error: Task "A1" is not a subtask of "A2".
But after a refresh of the page task "A1" is correctly displayed as a subtask of "A2".