Strack traces like these are logged on igniterealtime.org:
I have refactored the implementation, which among others prevents this stack trace (and won't close the connection when server- and peer-sided bookkeeping runs out of order).
merged. This is running on ignite now. I still see some occurrences where Openfire receives an ack with a value higher than kept locally, but now, the connection isn't terminated as a result.