I have this line in my ~/.gnupg/gpg.conf file:

comment ☃ ЦΤℱ—８　☕☂☄

I added it because of a Kontact (KMail 2) bug https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=754265 (also, with less context, https://bugs.kde.org/show_bug.cgi?id=248058). This makes the sending MUA set the MIME charset of the RFC822 message to UTF-8 instead of ASCII, due to the Unicode characters in the “Comment” field of the ASCII-armoured PGP message.

But I just found out that, when I set this, any PGP/MIME message gets broken.

Reproducible: Always

Steps to Reproduce:
1. echo 'comment ☃ ЦΤℱ—８　☕☂☄' >>~/.gnupg/gpg.conf
2. in Kontact, send a PGP/MIME encrypted message to myself
3. be unable to read it (Inline PGP works, as does using "fnord" as comment, which I used in “Expected Results” below) because, as you can see, the encoding is trivially wrong (= gets encoded as =3D3D instead of =3D)

Actual Results:  
From: Thorsten Glaser <t.glaser@tarent.de>
To: Thorsten Glaser <t.glaser@tarent.de>
Subject: test pgp/mime
Date: Tue, 25 Nov 2014 16:49:09 +0100
Message-ID: <5676877.O3l2Uj2cYJ@tglase.lan.tarent.de>
Organization: tarent solutions GmbH
X-KMail-Identity: 624161509
User-Agent: KMail/4.14.2 (Linux/3.16.0-4-amd64; KDE/4.14.2; x86_64; ; )
MIME-Version: 1.0
Content-Type: multipart/encrypted; boundary="nextPart1971662.MmlWDFlsHR"; protocol="application/pgp-encrypted"


--nextPart1971662.MmlWDFlsHR
Content-Type: application/pgp-encrypted
Content-Disposition: attachment
Content-Transfer-Encoding: 7Bit

Version: 1
--nextPart1971662.MmlWDFlsHR
Content-Type: application/octet-stream
Content-Disposition: inline; filename="msg.asc"
Content-Transfer-Encoding: quoted-printable

-----BEGIN PGP MESSAGE-----
Version: GnuPG v2
Comment: =3DE2=3D98=3D83=3DC2=3DA0=3DD0=3DA6=3DCE=3DA4=3DE2=3D84=3DB1=3D=
E2=3D80=3D94=3DEF=3DBC=3D98=3DE3=3D80=3D80=3D
=3DE2=3D98=3D95=3DE2=3D98=3D82=3DE2=3D98=3D84

hQIMA4lQwYleuNOzAQ//VYkwBTa1oEEL4Kd8/ErEsRTdW21uk8ee/G2s0DgIPoBJ
n1VV2TRheoG5bBI3K9xLEqMJaizWbdWaV8g3tNZpJB9+oibsBGUyZJO+bym07UnQ
iqMVFJ9iZ3iIAT+byNNVc4//t9MJJtrKg3r5HhcAB+eNPOJw+OFjN4KN+cuCxKE/
6sN0jhIRFaVacjgxiuXA0MbZV3T8vhg1kMrHDBmiV7MApnuxcZ+NBZSCxryHCuDI
31eFxW0wjPpOjTqy6rdtv2C5lEuQSbhFedMHawY0ZTYWwEIAGfKjVayGMCjhvCOa
KrVtSuIE2go05tDHYZhPlprdYlU8RhJ10K4SSp2iHPUnKt1tpQUQupaFFU/07GB4
arqzFpn7sbv8scMXOdSWsBX9u2uJNqqHzq2rAVWUqIK0SOotkqAF0Y+n0VYMajPQ
4MlhX8L40KReSHJVudGVMGiaLb98WYqH/EgSndojD/QjsJ4A2U9rsQumdinkLMfY
ITqP2uNHakHIVehA1XgPl72YggUKPi6WRheau9Jn+eTXh/h0/JKQlQVG/Y7x1VIt
SU7pmz4BeKiLtEvWsD5wRVBrOjoztG9AKu8jyXOq/tUvd4oEeT5McdBm7xsLwF8A
cmGyKR49IrFFa3e0Oe3XwX9G5KsHZrNakI2XjqmQpRQgRpw4afpZB7c7P7mIcifS
wKYBKm6xPdYfRtEoy6eIBJCMHjXcZKXtUZzVqSibMNaGTm4OAbgd/610dZR4Xp8j
lGGqeC/jqvHq7sKhImk56KLl3RRsKQY/JZ1ynIVy8lv0VdsboIniPDloJE5DWB20
6jpww7PAY8LmeqgbpQks8SC3+nYhn2dPcS2q05nIUk9qxA0XJZHiurOL/5hhIwYN
vWA7ec33BCnDGAbjYdfrKjnuUFqyX95FmGRGgW5PHEMuTzDPB1HQJnFKmfDkmQ8h
gtbd7fVw9HospOg+xgJp37viZ9yOqi3tRn9+PNz0cN6R8Kr/ZHK4sD709TM5a/IN
IwIvGCeI70c7W7DS/oMAUoXKht+y2ATxasAZ1O6xP9PLI3AYvac3tF4Ach6Vo/yD
TQ5VxWhvXThhJrCVPgAWGGBX5UFJ9bfVOeNwER6/YRGVUtEzdlGNRzW6siksj1oM
DarovPvbPsePs4ZnHZRwm5ulE31HzMPP
=3D3DOK3b
-----END PGP MESSAGE-----

--nextPart1971662.MmlWDFlsHR--


Expected Results:  
From: Thorsten Glaser <t.glaser@tarent.de>
To: Thorsten Glaser <t.glaser@tarent.de>
Subject: test defused pgp/mime
Date: Tue, 25 Nov 2014 17:06:28 +0100
Message-ID: <2010470.gc506rzj71@tglase.lan.tarent.de>
Organization: tarent solutions GmbH
X-KMail-Identity: 624161509
User-Agent: KMail/4.14.2 (Linux/3.16.0-4-amd64; KDE/4.14.2; x86_64; ; )
MIME-Version: 1.0
Content-Type: multipart/encrypted; boundary="nextPart23624681.54267B9MrA"; protocol="application/pgp-encrypted"


--nextPart23624681.54267B9MrA
Content-Type: application/pgp-encrypted
Content-Disposition: attachment
Content-Transfer-Encoding: 7Bit

Version: 1
--nextPart23624681.54267B9MrA
Content-Type: application/octet-stream
Content-Disposition: inline; filename="msg.asc"
Content-Transfer-Encoding: 7Bit

-----BEGIN PGP MESSAGE-----
Version: GnuPG v2
Comment: fnord
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=+Ttg
-----END PGP MESSAGE-----

--nextPart23624681.54267B9MrA--