Since the latest KMail version, I have this weird full-height black vertical column in KMail saying "HTML-message" (or similar, mine is in Dutch). Hovering it says something like "click to switch between HTML, plain email or calendar", and it has a hover-cursor. Clicking it doesn't do anything, however. I also couldn't find a setting to disable it. Is it possible to remove? I already use a toolbar button for switching between HTML and plain email (like it seems this is intended for?), which also makes a lot more sense to me than something you cannot move/remove and takes up lots of space.
*** This bug has been marked as a duplicate of bug 393421 ***
This is not a full duplicate, as I see it: the bar doesn't work for its intended goal (switching between HTML/plain e-mails).
If you can't click on it, it's because your message is html-only
but in that case, it doesn't show the message warning about displaying external references (tested with master)
For me, it doesn't matter if the email also contains a text part or not (I checked), clicking the bar never does anything. Also, the bar with "display external references" appears exactly if the email actually contains those references (so not if all images are attached), which is what I would expect. That also doesn't depend on if the email has a text part or not.