I am syncing my recurring Outlook.com tasks and they all appear in the Agenda list. However when I mark them as completed when the account sync’s a duplicate entry appears and the original entry is unchecked as being completed. The second entry is set to midnight the day the task is due. I’ve confirmed this happens for past due Activities as well as ones in the future.
To add onto this, I’ve downloaded the recent update today and the issue still occurs. As a workaround, I’ve found that if I delete the single instance of the reocurring task, when my account resyncs, it will reappear as a nonreoccuring and a reocurring task (2 separate entries) and i can mark both as complete and will be hidden from active view.