The scenario happens as follows. You have a write operation that writes K and it queues the update in IRAC queue.

(Thread1) The IRAC thread processes the queue and tries to send K to the remote site but it is in offline mode. The response is processed asynchronously and sent to a thread pool
(Thread2) State transfer is started, changes the remote site to online mode, and iterates over all entries to append them to the queue. However K is not appended since it is already there.
(Thread3) Processes the response from Thread1 and removes K from the queue.

Causes random failures in IracStateTransferTest