Domain running beyond boundaries source surface. So why is that?

Hi everyone,

At the university this week we started to work with Grasshopper so it is all new to me. I have bumped into something that seems strange to me. In grasshopper I've created a script that makes a surface with rectangular holes in it. The idea is to have a rooftop with glass panels which I can variate in size.

However something strange occurs. You can see in the picture that I have chosen two different surfaces as a sources for the build. The same scripts are running for both surfaces, but for one surface the script makes the domain in which the glass holes are defined bigger then the boundaries of its source. Both surfaces seem to have similar properties but differentiate in size.

So in my script the parameter surface is the source for 'divide domain 2'. Then both the parameter surface as the divide domain 2 runs through Isotrim. The result is a domain and rectangular holes that runs beyond the boundaries of my source surface in rhino.

What is going wrong and why?

with kind regards,

Matthijs