Exporting subD to STP Issue

I run into a something new to me. While exporting geometry done with subD into STP format I’m getting this strange result where all the surfaces which were neatly joined together in rhino, fully watertight, now after opening STP file are overlapping. In fact I shrunk all surfaces before exporting yet these guys somehow expanded in size. Red are rhino surfaces before export, black are post STP.
I have to admit I have no idea how to deal with this.
STP_Export.3dm (3.5 MB)

Hello- I do not see that at all here - does this look correct?

SubDBox.step (211.4 KB)


Thanks Pascal. Yes your box looks watertight.
This is my first attempt at exporting subd derivatives to step so no idea why would this happened to my geometry. I’ll look into it again tomorrow.

In the meantime I came out with a quick and dirty solution. Extract isocurves, use them to build NetworkSrf, join into solid. It seems to work. Step is returning fully watertight models.