Both images are the same operation. The first is a square cut diagonally. The second is the square cut into four straight lines.
I previewed the first one and thought it would look better as it is in the second one (and it does).
Breaking a shape creates new shapes, and you assign single shapes to an op - Breaking them makes new ones, and those ones don’t have the same shape assignments.
In your specific case it worked, because you were engraving along the line, but if you were doing a pocket, for example, breaking the shapes wouldn’t work in the same operation.
The behavior is common. In MM, you can use “Auto-use Layer” and then anything on the chosen layer will get used by the op, which would behave the way you want it to.
I think I understood the logic but thought this was unexpected as the Cut-Shapes Tool issue. I have used MasterCam in the past, but I can´t recall its behavior in these situations. Have to check an old PC if I have a running copy.
If I may, I´ll suggest maybe an option to brake or not brake…
Thanks.