Hi James, I'm not seeing any different code paths in there for Mac vs Windows.

Is the difference in behavior due to a custom construction plane being set on one system versus default world cplane in the other?

Because the plane returned by the offset factory's .getCurvePlane() function is used in the regular offset command as a plane for the pointpicker. When a custom cplane is set the origin of that plane returned by .getCurvePlane() will be the cplane's origin. It probably isn't good to use the pointpicker plane's origin point as a basis for an inside/outside point for offset. It may look like a good candidate because in some cases it's sort of a centroid point but not when there is a custom cplane set.

Instead of trying to generate a point inside a closed curve automatically it's probably better to give a point outside of everything's bounding box and then set a negative offset distance although that may not work properly until the next release when I can get this offset trim problem fixed.

- Michael