Same as https://www.mail-archive.com/kde-bugs-dist@kde.org/msg467018.html
The konq protocol is missing.
You can configure which engine is used by konqueror.
I have it configured to use “WebEngine”, and it is fine with “about:blank” as a url. But it complains about “bookmarks:”.
If I configure it for “webkit” or “khtml” then it is fine with “bookmarks:” but it complains about the “Be Free” start page and it complains about the “about:blank” page.
So, yes, there’s an inconsistency there.
If you want to use WebEngine, you may need to install “webenginepart”. I use it because konqueror is more stable with “WebEngine” than it is with “webkit”.
It works OK on my system.
I also use webengine as the backengine (which needs the webenginepart rpm) and have the kwebkitpart rpm installed which provides the webkit backengine. It might be worth giving them both a try to see if it sorts out your problem.