Why is the first CNC pass "facing" the part?

Snapmaker Luban
1

I have Luban 3.9.0 installed on my Linux laptop (that’s the only version I can get to work).

I have Luban 3.13.1 installed on my wife’s Surface.

With Luban 3.9.0 a CNC relief processed job just cuts the reliefed object.

With Luban 3.13.1 the fist pass is also doing moves that would “face” (i.e. flatten) the top of the material.

Is the 3.13.1 facing of the material intentional? Is there some way to disable it?

Thanks