This is an oversight, it was removed for testing purposes and it'll be added back in in the next build.
That said, your show is saved in the project directory automatically with any change you make. When you load Lightforge it loads right where you left off. These changes are only saved in the project directory and not in your actual ".show" file. Clicking "Save As" combines all the files (cuelists, patch data, settings, etc) in the project directory into one packaged ".show" file. Save As accomplishes exactly the same thing as Save would, except it prompts you for the filename you want to save as.