Instead of ordering elements, it snaps the GUI element with changed zIndex (to 1) to a top left corner of the window. Without modifying the value, all is fine. I have 2 camera in the scene: arc perspective and ortho.
well I guess a repro in the Playground will be a prerequisite to get an answer 
I totally understand, but I am a bit short on time now. I hoped there was maybe some extra step for GUI elements as opposed to regular 3D nodes. I will try to supply more info as I go with that project, hopefully able to detect what I am doing wrong here, if that’s the case.
My initial guess is that GUI elements are rendered via ortho camera and changing z depth “pulls out” elements away instead of in/out (hope that makes sense).
It should work out of the box (so this may be a bug ;))
Anything new?
not without a repro 