# Material glitches at joints when using Bevel modifier?

I've applied all my other modifiers and applied all transformations and I'm just left with a Bevel modifier for my object. And this modifier is causing weird glitches at joints that involve faces with different materials (see that odd little rhombus of red at the bottom right):

I've got Outer Miter set to Arc and have Harden Normals ticked. I'm pretty sure there are no geometry issues (overlapping edges etc.). Using Limited Dissolve and Merge by Distance doesn't improve the situation and in wireframe mode, you can see the mesh is super simple.

With the Bevel modifier disabled, everything looks normal:

And if I set Outer Miter to Sharp, I don't get the look I want at the joints but the odd glitch goes away:

So if I don't want Sharp joints, how can I solve the odd glitch shown up above? What's causing it?

Any help would be much appreciated.

Here's my .blend file (created using Blender 3.1.0)...

### Update

And I don't believe it's an n-gon issue either. If I add and apply a Triangulate modifier (with quad and n-gon method set to Beauty) I still see this issue:

The faces above are all triangles and I've increased the bevel amount to make the "glitch" even more obvious.

• If I APPLY the modifier, I can see where the material is applied incorrectly. With Strength set to -1, the closest material should be applied and there are errors. Mitre Outer changed to "Sharp" does a better job but not great. I would report this as a bug. You could also APPLY the modifier and manually apply the correct material to the errant faces until this bug is fixed. Mar 27, 2022 at 16:11
• Agree with @tempdev.. it looks like a bug. But at least a consistent, and therefore traceable bug. It seems to be in the 'Automatic' (-1) material offset setting, which should split the bevel down the middle at material boundaries. It's getting the boundary 1-off at the end of a patch/arc spread of faces. Have you reported it yet? Mar 29, 2022 at 18:48
• yeah agree definitely a bug with the automatic material offset, it gets confused by the boundaries. but maybe you want to consider using material offset index 0 or 1 instead of automatic, it actually makes it look nice as well. Apr 2, 2022 at 11:09
• Thanks for the feedback from everyone. I've now logged this as a bug - developer.blender.org/T97000 Apr 3, 2022 at 12:24