libsaslc TLS postfix client woes

[jgw%sdf.org@localhost]

Up until yesterday the following was providing Postfix SMTP client SASL
TLS authentication with my email provider's outgoing email
server (configs have been sanitized for public posting):

  #/etc/postfix/main.cf
  myhostname = beasty.sleepy.cat
  mydomain = sleepy.cat
  smtp_generic_maps = hash:/etc/postfix/generic
  mynetworks_style = host
  alias_maps = hash:/etc/mail/aliases
  relayhost = [smtp.acme.com]:submission
  smtp_sasl_auth_enable = yes
  smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
  smtp_sasl_security_options = noplaintext, noanonymous
  smtp_sasl_tls_security_options = noanonymous
  smtp_tls_security_level = may
  smtp_sasl_type = saslc

  #../generic
  me%beasty.sleepy.cat@localhost     me%acme.com@localhost

  #../sasl_passwd
  [smtp.acme.com]:submission	me%acme.com@localhost:secret_passwd

Did chmod 600 for the sasl_passwd file and ran postmap(8) run on generic
and sasl_passwd for DB file generation, then checked with 'postfix check',
then reload configs with '/etc/rc.d/postfix reload'.

Anyway, something has changed sometime since my previous -current update
dated ~May 2015; after upgrading to -current dated Aug 22, 2015 the above
configuration no longer works.

Below appears to be the pertinent bits from /var/log/maillog; date prefix
removed for clarity:

  ..
   beasty postfix/qmgr[7099]: 1AFE11F1FA9: \
    from=<me%beasty.sleepy.cat@localhost>, size=290, nrcpt=1 (queue active)
   beasty postfix/qmgr[7099]: warning: \
    private/smtp socket: malformed response
   beasty postfix/master[5621]: warning: \
    process /usr/libexec/postfix/smtp pid 7139 killed by signal 4
   ..
   beasty postfix/master[5621]: warning: \
    /usr/libexec/postfix/smtp:bad command startup -- throttling
   beasty postfix/error[5878]: 1AFE11F1FA9: \
    to=<someone%somewhere.com@localhost>, relay=none, \
    delay=1.4, delays=0.16/1.2/0/0.07, dsn=4.3.0, \
    status=undeliverable (unknown mail transport error)

I'm hoping someone can point me towards a solution or work-around
so I can go back to using the native tools for mail relaying.

Jeff

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

 This email has a PGP signature attached; verify
 using PGP public key at http://jgw.sdf.org/pgp/

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
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=KFMw
-----END PGP SIGNATURE-----