In KB http://support.microsoft.com/kb/2707146 we describe a problem with IRM-protected messages, which were journaled and forwarded to an external contact for Exchange 2010. In that Knowledge Base Article we stated, that we fixed the problem in Update Rollup 5 version 2 for Exchange Server 2010 Service Pack 2.
Unfortunately this fix was not carried over into Exchange 2013 and recently we received the request from a highly valued customer, to fix the issue also in Exchange 2013. This fix request at the first attempt was rejected due to mainly high complexity of the fix and to at that moment limited applicability (not many customers have reported the issue). Symptoms and cause from the KB article are also valid for Exchange 2013 (currently at Cumulative Update 3 - see http://www.microsoft.com/en-us/download/details.aspx?id=41175)
We are preparing a public KB-article about that fact, which is planned to be published later this year. Till that moment this Blog post can be used as a reference point. We hereby encourage customers and partners, which encounter the same problem with Exchange 2013 and do not want to ignore that circumstance, to either open a Support Service Request with Microsoft, document this circumstance in the comments section of that post and/or send a mail to appssrv at Microsoft.com (preferably with the support case number).