Clicking the fullscreen button in the 3.0 release of DA doesn’t work as expected. DA does go fullscreen but not in a new space like other apps, it takes over the main screen hiding the Finder. You can’t get the menu back by moving the mouse to the top of the screen which means that you can’t return from fullscreen mode either.
If you use Mission Control’s overview then click on the first screen then DA returns with the Finder’s menubar, not its own. Clicking on DA’s window will hide the Finder menubar but not give you access to DA’s menubar.
The only way to return back to normal is to type Command-Q to quit DA.