Body not displayed for S/MIME signed messages

Mails from a certain contact of mine usually have the following body:

Content-Type: multipart/signed;
 boundary="=_MailMate_7575846C-172C-4EB0-A42D-0C90D9D4FF5E_="; micalg=sha1;
 protocol="application/pkcs7-signature"
(last header line)

This is an S/MIME signed message (RFC 5652 and 5751).

--=_MailMate_7575846C-172C-4EB0-A42D-0C90D9D4FF5E_=
Content-Type: multipart/mixed;
 boundary="=_MailMate_4A5B0074-2492-490F-A37F-7CBD4337AE09_="


--=_MailMate_4A5B0074-2492-490F-A37F-7CBD4337AE09_=
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

When opening such a message in Conversations view, nothing of the content is displayed, only the header line and the “signed” button/icon. Below, nothing is shown.

[SimJoSt]

Same here. Nightly version of Enigmail didn’t help.

Edit: Some signed messages are being shown correctly. I can make the body of the buggy messages appear in Conversation with the following trick: right click on message in list -> open in new window (classic viewer in new windows shows body correctly) -> close window -> if message is open in conversation view, switch to a different conversation -> switch back -> tada! Message body is shown correctly.

[Black-Pixel]

I had the same issue with Thunderbird 52.7.0, Enigmail 2.0, and Conversations 2.13.4 on Windows 10.

To fix the issue I’ve first disabled Enigmail, removed Conversations, and re-enabled Enigmail to check if the mails still work. Then I have re-added Conversations. Everything seems fine so far and the E-Mails are being displayed properly.

I believe the issue is really the order in which the addons are added. The proper order should be Enigmail first and Conversations second.