Today, Apple released an update for iOS which supposedly fixes, amongst other things, some Exchange-related issues. The release notes of iOS 8.3 mentions the following Exchange-related fixes:

• Exchange out-of-office message can now be edited separately for external replies.
• Improves recovery of Exchange accounts from temporary connection problems.
• Fixes an issue that caused Exchange meetings with long notes to be truncated.

As for any update, I’d recommend to thoroughly test this in a test and acceptance environment first, prior to allowing access to your production environment. Apart from potentially blocking the new iOS, monitor the support forums from Apple and Microsoft for related issues. To block a specific version of iOS, consult this page.

More information on known issues with Exchange ActiveSync and 3rd party devices can be found in KB2563324.