Hmms.. in unregistered version all timeouts are disabled => if server does not receive proper connection closure (ssl_shutdown()) - it hangs inndefinetely. Neat, uhh?
What comes to FD_CLOSE - I'm quite confident that all data is being processed properly. Also FD_CLOSE should not occur in SSL mode before SSL_shutdown() has returned 1. If SSL_shutdown() is not called at all, some data may/will be lost.
Edit: I tried with smartftp, and did not notice any problems (timeouts disabled)