Editing and saving existing projects. All changes lost!

I have a projects i created that I wanted to use for a new event. I opened it, changed what I needed to change and then looked for a way to save it as a new project. The only option I could find was to "duplicate" the project and save under a new name, which I did.
As soon as I saved it, all of my changes reverted back and I now have two copies of the identical, original project, under differerent names! 
There's NO "undo", so I've lost what I did, and I don't want to have to create the entire project from scratch, because it took ages to do. I wanted to use it as a template that I could just update whenever I wanted!