If the optimistic locking version check fails, the version checking BeforeTransactionCompletionProcess is not removed from the action queue, so if I try to commit another transaction in the same session, the version check will fail again, and therefor the whole session can't be used for writing any more.

Simplest solution would probbly be clearing the BeforeTransactionCompletionProcess and AfterTransactionCompletionProcess (I'm quite sure they'll queues in the ActionQueue.clear() method.