It's been a long time since I've posted anything here. We've been busy - and perhaps I've been playing a bit too much Guild Wars 2. ;)
Recently I added a third screen to my system, and this only made the existing multi-screen issues I had with KDE even worse. Finally, I decided to do something about it, hunting down each issue one by one and fixing it. This post is just to serve as a guide to fixing these problems.