The "view source" action doesn't really view the source of the message anymore, but the source after being processed by the objecttreeparser. This is noticeable when the objecttreeparser modifies the mime structure. It should show the real source of the message, as it is in the storage.
SVN commit 1080139 by tnyblom: Show the unparsed source when displaying message source. BUG:223493 M +1 -1 viewer_p.cpp WebSVN link: http://websvn.kde.org/?view=rev&revision=1080139