What OS are you on?
Does the icon in the top right change from red circle to unlocked to locked at all?
I cannot reproduce this, and you should be able to change even with a background image. What background option are you using (Stretch, centre, tile)?
The z-direction is for every image. No longer has to be in the order in the xml file. 0 is top, and 1 is the bottom. You can do greater than 1, but 0 is always top and the larger the number the farther back it is. Industry standard is 0.0 to 1.0 though.
And for the edit part, what do you mean? You mean not having the windows be forcing "ontop"? Currently they are programmed as dialog boxes. Basically it pauses the main code while the window is open. Instead of events firing back and forth and again room for error and instability. I have never been strong with event programming, and I dont want to comprimise the stability of the new program because of it. Or is this not what you mean?