I know you’re busy with Rhino 8 reaching Beta, but I just wanted to bump this to see if you’d had a chance to look further into the behavior.
Thinking about this behavior further, it may not be a bug per say: a pure untrimmed NURBS surface doesn’t have edge information so my guess here is that we’re getting a silent call to retrieve the underlying surface. However there’s nothing to warn users that this is happening. At the very least grasshopper should be showing a warning message on nodes when this conversion happens so that users know that they have lost data in the conversion process.
This behavior showed up in another issue today: "Baking" Trimmed surfaces using Rhinocommon, where the issue was that the type hint for a python script was casting breps to surfaces and throwing out the trimming information in the process.
Thanks,
Cullen