CreateBooleanUnion returns a boolean difference?

Hi All
I’m new to c# and rhinocommon and am working my way through some of the functions to get some practice.
I’m having a problem with one particular case of Brep.CreateBooleanUnion- it seems to return a difference rather than a union.
I have included a file with two examples. One uses geometry generated from GH components and works well, the other uses geometry entirely from a short script and is the one that returns a difference.
I’m quite certain that the parts I am trying to join are closed and clean, with normals pointing the correct direction, and that they are organized within the list properly.
What am I missing here? I’ve spent some time digging through the forums but can’t seem to find a matching problem.

Thanks in advance,

Lucas (9.2 KB)

right before you do any brep solid booleans, you can check the SolidOrientation property and flip as needed

if (mybrep.SolidOrientation == BrepSolidOrientation.Inwards)
} · RhinoCommon · BrepSolidOrientation Enumeration

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Thanks for the assist!