Why some lines get merged into one line while others don't

Grasshopper
1

This is a planar surface with vertices shown.

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I want to divide lines #1~#3 and to recreate the surface. The result shows that #1 is divided and it’s subdivided points become the vertcies in the new surface; #2 and #3 are divided in GH, but the subdivided points DO NOT become the vertcies in the new surface. It seems to me #2 and #3 are merged individully again during boundary surface creation, so subdivided points are removed.

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1.gh (25.5 KB)

2

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I guess deconstruct brep was made to not break up lines with internal points
If you explode the edges, those #2 and #3 do get broken down further.