corner rounding only works right when two of the 3 dimensions is 0. In essence, there is a check to in each of the 3 shapes to see if one of the 2 pertinent dimensions for that shape is 0...if so...shape is hidden. other subshapes behave normally. So in essence rounding really works for "planes".

The problem stemmed from the fact that each subshape has different edges so the rounding is respective to their edges. So rounding a 3D gets you rounding in 2D along 3 axis (sort of double "bumps" on each corner where subshapes meet).

If you want to build something 3D with rounding, you might want to look at the manifolds. They will allow you to round corners and arc the edges. Use several to build your 3D shape (they have light source if I remember correctly as well). When down, group them and go.

I still have not gotten around to making manifolds like "legos" yet...aka connect them up via connection points.