Thank you for this answer! It helped me with a related problem. It’s a work around for me, but it works.
The problem, if anyone knows how to fix it where it starts, is this. I’ll sum up.
I created a creature in zSketch, converted to polys, and got to where I wanted to extract some sub tools to create armor. I masked off the chest area, exactly how I wanted the armor to start, and hit extract. When I hid the first mesh to look at the extract, there was a bunch of geometry also extracted from other areas: areas I had not masked off.
Now, I know that I can hide those unwanted areas and use DelHidden.
Those areas shouldn’t extract like that at all though, so it would be nice if that could be stopped… but short of that, the work around is a big help.