Hmmm, it appears that when a cache is configured with REPL_ASYNC and repl queue, a non-serializable object being replicated will fail silently. It would appear as nothing replicates but the error will only become apparent when TRACE is enabled.
This is not very nice and would have a direct impact in AS use case, cos web cache is configured this way and users often put stuff in the HTTP session that cannot be replicated.
This would cause issues amongst users. Verify what happens with std REPL_ASYNC (I think here the serialization still happens in same thread and so the users would see it). Async marshalling would also need to be checked.