Issues with BREP solid difference (inconsistent result)

Hi all - I’m pretty new to GH and wonder if I’m missing something here.

I’ve got a series of BREPs, essentially a cluster of cubes generated from previous operations. I want to subtract an extrusion from the set, so that it effectively cuts a tunnel through the mass of BREPs.
It works perfectly using Rhino’s boolean difference, and Grasshopper’s solid difference works when I bake and re-reference the BREP sets from Rhino, as shown.
However when I use the BREPs outputted from previous operations within Grasshopper, each trimmed BREP includes an attached copy of the extrusion as shown.
Am I missing something obvious? Any advice would be appreciated.

Thanks a lot,
Ted (288.5 KB)

there must be something weird happening with those internalized breps (flipped normals?) because if you explode and re-join them, then it works smoothly (293.0 KB)

[edit] I confirm, for each and all the internalized breps, they all have face normals oriented inwards

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That makes sense, I must’ve done something weird! Thanks a lot, mine works too now!