Bug: Simple merge coplanar faces failure

[diff-arch]

Here’s another geometry that fails in 7.2.21012.17002:

geometry.3dm (3.8 MB)

(I’m not looking for a fix! Just reporting.)

Rhino makes it hard to detect corrupted models! (Prev. title: [BUG] STL export corrupts some models/meshes!)

Hi, I think there’s something wrong with the STL export in Rhino 7 for macOS! I’ve noticed a couple of times already, when exporting STLs for Cura - an open source 3D printing slicer - that it shows an error message (“Something wrong with your model…”), when importing the STL. [Screenshot 2021-01-23 at 17.06.56] This very simple and clean geometry is a closed solid polysurface, and gets somehow corrupted when exported. Non-manifold edges get produced! [Screenshot 2021-01-23 at 17.10.52] R…