Hi James,
I'm using the file I posted(http://moi3d.com/forum/index.php?webtag=MOI&msg=7777.987)
Just added a sphere and trimmed it on it's seam to make a dome surface and named it S8.
From the photo you can see the tangled result of the dome and when S7 was next applied
you can see it is also wrong.
I noticed the surfaces spike to drawing origin.

Barry