See https://github.com/jaymzh/pius/pull/96

commit 4dba0bf75ab351969622f7b9c38484657411a528
Author: Martin Kletzander <nert.pinx+github@gmail.com>
Date:   Thu May 17 17:55:27 2018 +0200

    Don't fail on ENCRYPTION_COMPLIANCE_MODE line from too new GnuPG (#96)
    
    GnuPG started printing information about encryption compliance in [commit
    f31dc2540acf](https://dev.gnupg.org/rGf31dc2540acf7cd7f09fd94658e815822222bfcb)
    and since then signing with pius fails.
    
    Closes #95
    
    Signed-off-by: Martin Kletzander <nert.pinx@gmail.com>

diff --git a/libpius/signer.py b/libpius/signer.py
index 3c7262f..13013bb 100644
--- a/libpius/signer.py
+++ b/libpius/signer.py
@@ -45,6 +45,7 @@ class PiusSigner(object):
   GPG_PINENTRY_LAUNCHED = '[GNUPG:] PINENTRY_LAUNCHED'
   GPG_KEY_CONSIDERED = '[GNUPG:] KEY_CONSIDERED'
   GPG_WARN_VERSION = '[GNUPG:] WARNING server_version_mismatch'
+  GPG_ENC_COMPLIANT_MODE = '[GNUPG:] ENCRYPTION_COMPLIANCE_MODE'
 
   def __init__(self, signer, force_signer, mode, keyring, gpg_path, tmpdir,
                outdir, encrypt_outfiles, mail, mailer, verbose, sort_keyring,
@@ -431,6 +432,9 @@ class PiusSigner(object):
       if PiusSigner.GPG_ENC_BEG in line:
         debug('Got GPG_ENC_BEG')
         continue
+      elif PiusSigner.GPG_ENC_COMPLIANT_MODE in line:
+        debug('Got ENCRYPTION_COMPLIANCE_MODE')
+        continue
       elif PiusSigner.GPG_ENC_END in line:
         debug('Got GPG_ENC_END')
         break