As far as I can tell, there is no obvious way to save your work that you have done in the Games Master Editor when you exit (although the leave option is "Save and Exit". )
This means that you can spend quite a lot of time placing assets and AI, and then have to start again when you go back to the Games Master Editor. It would be great if there was a way to save all that hard work.
(Apologies for all these bug reports, but I really love DayZ & Arma, and think Reforger on Console will be amazing, and want to help it get there!)