The blend that you see is done in Rhino. Delete it and attempt it in MOI and you get a weird result.
The cut-out was swept with two rails and then cut with the curves that you see in front of the surface.

I'm very well aware that there is a different way of creating the cutout (by projecting a blend of the two rail curves and then trimming) in a way that the blend looks cleaner and is possible in MOI, but my objective is to try to expose certain vulnerabilities in the blend command so that it can help Michael fix it in the next revision