proftpd的ssl日志报错

proftpd的ssl日志报错：
May 20 16:36:41 mod_tls/2.1.2[4837]: SSL_shutdown error [1]:
  (1) error:1409F07F:SSL routines:SSL3_WRITE_PENDING:bad write retry


找了一下：
http://forums.proftpd.org/smf/index.php?action=profile;u=5951;sa=showPosts