Hi gizmo - what I wrote above was for the pad2 example - for pad1 it is different, like Manz wrote above there is a problem there with the seam edge.

It looks like a bug in extrude, the extrusion is also trying to extrude up that seam edge which is not proper.

What I mean is for pad1 if you use Edit/Separate on the object after you have extruded it and then move away the top surface, you will see this:




See that extra vertical surface that is on the inside of the shape (I have selected it here)?

That shouldn't be there - it looks like a bug in the surface extrude that it is creating that, I'll see if I can fix that up.

If you do what Manz wrote above to get that seam edge out of the way from your base surface before extruding it, then you should be able to avoid this problem.

- Michael