Hi NightCabbage - really the easiest way to manually make a sphere is to have a 180 degree arc and then use Construct / Revolve to revolve it around an axis, with the pivot axis being the line between the arc's end points.

The "scaling rail" option in sweep tends to be rather sensitive to areas where the scaling rail collapses down and actually touches the main rail like you have in this particular case.

Also the scaling rail should cover the entire length of the sweep - if the scaling rail is a little shorter than the rail then it would also make the kind of result that you show there so that may be a possibility as well.

It's hard for me to know for certain without seeing the actual 3DM model data - if you have problem it actually helps quite a bit if you would also post the 3DM file instead of just a screenshot, because then I can more closely examine the geometry to see what is going on.

Check out this previous post for some more description and illustration of how the scaling rail option works:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2681.3

Hope that helps!

- Michael