There is a couple of bugs in compositing support in notion wm now. At first alpha channel for color seems didn't get correct value, so you get artifacts when reparent something in "root" window, for example if you do vertical split you get a "copy" of old window without reparenting instead of wallpaper's background. I set background with hsetroot. Also if I turn off transparent_background in theme file all works well.
Also there is no correct work of transset-df, so it seems that transparent attribute set to all windows (include root?) instead of only one. But dmenu or dunst with opacity setting works well. Manual setting of _NET_WM_WINDOW_OPACITY didn't get affect on window at all.
I tried compton for it.
Once I tried to find a bug, but not all old versions did compile now with new lua libs(?), so I can't bisect bad commit.