Hi,
well, I think MLO positions itself as a personal task management solution and not a professional project management software.
In these terms, the "Project" in MLO means quite a different thing than a usual business project. The most prominent use case is GTD system, which defines a project as "any task, which requires more than one step".
In this sense, I can easily see how I would want to see the project "Not started", even if few tasks are already complete. Perhaps I would want to have few preparation tasks at the beginning of the project. For example, if my project would be "buy a car", maybe I would want to complete few things like, "decide do I need a car" or "look for options", but still don't have a project as "Started".
If the project is just a list of tasks and not a business project with clear definition, then the "Project status" property becomes just one more property of this item, which you can set up in any way you want, depending on your productivity system.
Of course, I would agree that it would be good to have a possibility to turn this automatic function on and off. But that would mean one more setting in a already cramped settings window, and of course, some cost for its implementation. I assume that the developers decided that it's not worth it.
Regards,
Domas