One of the benefits of Apple's iOS devices such as the iPad and iPhone is that you can upgrade to the latest version as soon as it comes out. Being on the cutting edge is usually a good thing, but sometimes it can come back to bite you. If you are connecting to an Exchange server for mail and calendar services, the latest version of iOS has an unpleasant surprise in store for you.

Reports started surfacing in late January about excessive logging on Exchange servers caused by the upgrade to 6.1. A report on Microsoft Technet states:

I had a user upgrade to 6.1 and immediately after he finished, his phone/IPAD started causing excessive logging on the exchange server. I found the problem by using exmon and saw the CPU utilization in conjunction with high session count. He shut down Outlook and the problem remained. He turned off his iPad and the problem went away. The only change he said he made that morning was upgrading to iOS 6.1.

This problem has been confirmed by many sources. Windows IT Pro's Tony Redmond reports:

I’ve picked up a few other reports that cannot be publicly attributed at this point that also refer to excessive transaction log generation after iOS 6.1 devices are introduced into Exchange 2010 or Exchange 2007 environments. I assume the same is true for Exchange 2013 as the underlying cause is likely to be in Apple’s mail app code that calls ActiveSync to synchronize with a user’s Exchange mailbox, with some indications being that the problem is once again associated with calendar events. You’d think that Apple would have learned after the iOS 6.0 calendar hijack fiasco.

Until the bug is fixed, corporate users are advised to not upgrade to iOS 6.1. For users who have already upgraded, though, there is no way to revert to the previous version. IT administrators have no control over when their BYOD users upgrade, so many of them have resorted to blocking iOS 6.1 from accessing Exchange as a temporary mitigation to prevent server outages for everybody else.

Apple has not yet acknowledged the problem or stated when a fix might be available, but hopefully it will be patched soon. Meanwhile, early adopters will have to access their calendars somewhere else.

Updated February 15th: Microsoft has more information about the problem in a Knowledge Base article, and Apple has also acknowledged it in a support note. Sources say that a fix is on the way in version 6.1.2.