I would not count on it.
@Rhino_Bulgaria - just use the RebuildMesh command with PreserveTextureCoordinates=No and PreserveVertexColors=No.
Unremovable material Fixed.3dm (132.4 KB)
– Dale
I already tried that multiple times, in any possible combination. All the available Rhino tools I tried so far still can’t fix the visual bug.
See my attachment above…
Can you try the ! _RebuildMesh command on the 3dm file I posted several hours ago in post #16? 
Also, if you try the first 3dm file in post #18 and apply ! _QuadRemesh to it, you will notice that it will produce bad meshes most of the time. The bug is caused by this particular tool in Rhino.
@Rhino_Bulgaria - The RebuildMesh command isn’t going to fix this mesh. @nathanletwory pointed out it’s issues.
You can fix the manual way - extract points, delete faces, append faces.
Rebuild mesh normals fails - Fixed.3dm (52.9 KB)
– Dale
I opened your .3dm file:
https://discourse.mcneel.com/uploads/short-url/hIBuJIJgYUu9K30orGEHFJMvfk0.3dm
then exported the mesh to a .obj file and finally imported it with my mesh script. The script analyzes the mesh and puts identified issues on separate layers. One of these is non-planar quads. For your mesh this looks like this:
This shows 9 out of the 10 mesh faces are non-planar by 0.021 (red faces) to 0.35 (purple face). The edges of this mesh are as big as 81 so the non-planarity is only 0.026% to 0.4% of the longest edge length. The vertex coordinates range up to 1200 so the floating-point noise floor is around 0.00012 ( = 1e-7*1200). Thus, the non-planarity is >200X bigger than this. So, the non-planarity could be intentional.
I wonder how this mesh was created? Was it generated manually or automatically? Do you need the mesh to be non planar?
Here is the .3dm file used to generate the picture above if you want to play around with it.
UnremovableMaterialNonPlanarQuads.3dm (82.4 KB)
Regards,
Terry.
As I mentioned at least twice in my previous posts above, that mesh was created in Rhino 7 via the “QuadRemesh” tool using the first attached 3dm model from post #18 as an input geometry. It’s not imported. 