Hi Leonard, yup I think you've got it - basically the history mechanism is set up so that you could edit the original curve or the surface it is projected on to and see the projection update. It's possible for that update mechanism to get in the way but if it does you can disable it with that Edit > History command.

But like Burr mentions if you want to flatten something it's quicker to go to a side view and use the edit frame - here's a demo video:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3378.4

- Michael