The CPProj is designed to be the pipeline PLUS the location and metadata of all the associated images; if you clear the images but don’t save it afterward, every time you open the .cpproj file the images will still be there. You can instead export the .cppipe (which has just the pipeline but no images) by going to File->Export->Pipeline (you can even tell CP to automatically save a .cppipe copy of your .cpproj every time in the File->Preferences menu). When you open the .cppipe, no images will be associated.
We’re glad to hear the software works so well for you! Best of luck.