I know from my old win 8, that sometimes changes in decor8 not applied, until I restarted the win explorer. No matter how much I played with the config window. After that, changes got applied right away, till it got stuck again.
That still happens for me on 8.1.
So it actually isn't new problem, I just have not used parallax scrolling before, which is affected. It also isn't a specific win 8.1 problem, which I first thought of.
Now I need to do more (and also luck), to get it working again. Which is starting to be a hassle, now that I encounter this state more often due to a not working parallax scrolling. I make changes there rarely, so it wasn't a big deal before.