FCPX 10.1.3 - How Do I Copy Project?
To freeze your current state of work you need to load a Library and right click on a Project. Important is you need to choose Duplicate as Snapshot. Only then you make a protected copy of your current work. 
Here is why: When you have compounded clips in your project, these clips living outside of your project, available to all Projects in the Library. When you Duplicate your Project only, any change you make inside a Compound Clip is rippling to any Project what is a duplicate to this Project you working on and has this completed Clip in your timeline. 
Here is a link to a video that shows the effect. Watch maybe a couple of times as the guy is kind of fuzzy on his explanation.
Duplicate vs Duplicate as Snapshot