When using MINA in JAMES we saw malformated packets when processing POP3. This was a cause of a bug in our code which wrote a "null" object to the session. Unfortunally MINA don't throw an exception in this case and just write garbage to the session. We only found the bug because we have a netty implementation too which throws a NullPointerException in this case.
I think MINA should do something similar..