Hi Nick - are you using the "Mode: Closest Pt" option for the projection?

That mode unfortunately does not really work that well - it calls a function in the geometry library but it turns out it only works very well if the curve is already pretty close to the surface to start with.

In your case here, it's making some really bad quality curves that are sort of wiggly and have some areas that are kind of like little curly-cues - that kind of thing where a curve crosses over top of itself will tend to really confuse trimming when it tries to determine inside and outside regions of the trimmed up area. When you get things like holes that are filled strangely that's usually what is going on (self-intersections in the curves).

So that particular Closest Pt mode is just too junky to get good use of right now, you have to do a straight direction projection to get good results for this currently.

I'll be writing a new closest point projection function in the future to replace the one in the geometry library that does not work well for this purpose.

- Michael