Just received this notice at work:
Outlook Calendar Issues with iOS Devices (iPad and iPhone)
There is currently an issue with Exchange calendars on devices running iOS 6 (iPhones and iPads). The issue manifests itself when a meeting recipient declines an invitation, which then cancels that meeting for everyone. Apple and Microsoft are aware of the issue.
For now, until the issue is corrected, we recommend users with iOS devices manage their calendars from the Outlook client on their computers.
Irritating. Even more irritating that I hadn't heard about it yet through all of the Apple channels I read on a semi-regular basis. It's been out there for a while, however. (TUAW, MacRumors)

Hi,
Sorry to bother you with this, however I would like know if you may know if this has been resolved.
Thank you in advance for your attentions to this concern.
CB.
Hi Carlos,
From what I’ve heard, there is no fix yet. It’s a “known issue” for both Microsoft and Apple. I don’t even know if they know whose bug it is to fix.