Third-party calendar sync with Microsoft accounts returns after week-long outage

Microsoft has now fixed a fault that stopped third-party Windows Phone calendar apps from syncing with Live\Hotmail\Outlook accounts.

It was the second sync outage this month and lasted six days.

Could it have been Microsoft doing some backend changes ready for the release of Windows Phone 8.1? Or could it be related to today's expected unveiling by Microsoft of Office for iOS?