Re: Dual Screens
>Never noticed that behaviour in KDE5
No you haven't grasped it, KDE doesn't properly remember or calculate where it's windows placement is in X on dual screens when opening.
Compiz 0.8.12 handles this very well even under KDE5 unfortunately there are a couple of issues with the taskmanager bar auto-hide not working and preview windows on taskmanager not working either. Additionally when you want to do replace --kwin_x11 to return to kwin when you have compiz running systemd starts eating CPU cycles and Kwin's windows decorator crashes. I've only recently upgraded for Opensuse 13.2 to Leap 42.2 because I knew from past experience (KDE3 to KDE4) that KDE5 would bring a heap of issues and sadly I wasn't wrong.
I'm seriously considering Gnome (or Mate) which for a very long time (well over 10 years) hardcore KDE user is a sad day.