Recently, a bug in Apple's implementation of ActiveSync in IOS 6 caused issues where someone would erroneously take ownership of a meeting when opening an invitation as a delegate. This phenomenon - also known as "meeting hijacking" - caused quite some issues all around the globe.
It even came that far that Microsoft's Exchange team made a public announcement for that issue, providing several workarounds (as it was Apple's responsibility to solve the issue): http://blogs.technet.com/b/exchange/archive/2012/10/23/ios6-devices-erroneously-take-ownership-of-meetings.aspx
Now, a few days ago, Apple released an update that should solve the issue: http://support.apple.com/kb/DL1606
I haven't been able to test the update myself, but people are reporting that the issue is indeed solved. However, the autodiscover issue/bug apparently didn't get solved. This bug causes autodiscover to fail if a user's email address and UPN don't match. Have a read at Steve Goodman's blog for some more information: http://www.stevieg.org/2012/11/ios-6-0-1-update-available-including-exchange-meetings-bug-fix/
Michael Van Horenbeeck