@eugen-b,
Thanks for getting back to me, as I'm in the state of panic now! Not only this update screwed several of my computers, but it also destroyed my wife's computer. So I'm really in a big trouble now! I installed encryption through the installer, and not manually. I'm not a technical guy, and primarily a GUI user, and that's why I'd chosen Manjaro, because your don't have to be a computer guru to use it.
In any case, I have the Manjaro KDE 15.12 on a stick, that I can boot into it, but I don't see how to install the package downgrade. So how can I install the downgrade package?