The tutorial doesn't really tell you how to do it in the right order. You create the world, edit in ZeroEditor, then you munge. When you munge the level, it's actually compiling the level's source files and saving the new files to your AddOn folder. Saving in ZE just saves the source files. It doesn't compile the changes.
"Do you not know the pain you will suffer for this impudence?" - Ba'al