I really didn't know what to put as a title, so...
We upgraded to 2014 from 2012 sp2 on a SLES 11 SP3 at the end of May: One domain, One PO and all agents on the same server (VM on XenServer 6.1).

First thing I've noticed and I have an SR open, is that SOME email addresses have gotten corrupted in the Frequent Contacts Address Book.
In GWIA it shows two or three strange characters in the beginning of their email address and, of course, the email is undeliverable.
I've gone in the user's Frequent Contacts address book and position the cursor at the beginning of that email address, then I press the Delete key.
The first visible character doesn't get deleted! After I save it and have the user send out another email to that user, it works!
These email addresses are to people outside of GroupWise. If they ever figure out what is the cause of it I will report back.

The other issue, and so far I've only had one person point it out to me, is on a reply message the body of their original message has strange characters added through email, but not in the reply message area. Have you seen this? I'll keep an eye on it to see if they are from a specific user only or more.

Gosh, I feel so much better letting my secrets out! ;>)