Past due recurrence Todo doesn't recur?

Dear List,

I'm using Kontact (4.3.0 now and since long before) and I don't
understand why a past-due recurrence Todo item doesn't recur after
completion.

If a recurrence Todo is completed before due, its due date is updated
correctly. But when I complete a Todo item that is already past due,
it remains in "Completed" status and due date is not updated, thus
doesn't recur at all. Is this the designed behavior, or a bug, or my
fault on using it?

Thank you.

-- 
Li, Yan