How to Split a complex polysurface into 2 pieces using a closed curve?

I try to cut a complex polysurface with a closed curve.
Trim can’t cut.
It seems to work if I use the _Split. New edges are formed but the polysurface is still a closed solid.
But at the same time, I see the result on the command line: One polysurface split into 2 pieces.

How to make these two pieces separate, without using the _Explode and delete excess surfaces in manual?

Split complex surface.3dm (1.2 MB)

Hello- I agree, this is not right - my guess of the moment is that the problem arises because the trimming curve is coincident, here and there, with face edges. I’ll put it on the pile for the developer to have a look.

RH-69743 Split: partial split



Thanks, Pascal.