Created attachment 99419 [details]
example message to reproduce the bug (mail addresses changed, Received:-headers removed)

I recently upgraded to KMail 5.2.1 from the KDE Applications 16.04.1 release.

This is a regression somewhere between KMail from KDE Applications 15.12.2 and 16.04.1.

The commit notifications sent out by launchpad are Content-Type: multipart/mixed with two sections: 1. a text/plain part that contains the commit message etc. and 
2. a text/x-diff section that contains the actual change in unified diff format
(I'll attach a sample mail)

Since the update to KDE Applications 16.04.1 (I never tested 16.04), KMail displays those mails with wrong content order:
1. the diff
2. the diff, again
3. the commit message

Expected behaviour (worked in 15.12.2): display the mails in the order as defined in the mail, which means
1. the commit message
2. the diff