Hi Henri,
Sorry for the delay in answering, but here is a holiday and I was for a walk ;o)
I have checked this, as I couldn’t recall a time where HyperNURBS was able to affect a second row. That is the key point of my idea (a decade+) ago about the supportive edge.
The cube had only six polygons and the HN was set to 3;3 (edit/render subdivision) Left R11.5—Right images R16.
So, I opened R11.5 and R16, and started each time from the scratch. I can’t reproduce it. I can go back to R8 if needed or even to R4 (if I find an old OS as well, thehe, but I can’t really remember if R4 had at all HN). However, I believe you can share an expample file—and I’m happy to explore it.
All the best