Multiple decalGeometry to same position not displaying second decal

i’m trying to apply alternate decals to the same position, depending on the underlying color (dark base, light decal; light base, dark decal) using decalGeometry. When the second decal is created, it simply doesn’t appear. This fiddle illustrates the issue.

I’m creating a black decal, then a red one and then hiding the black mesh. I’d expect the red one to be present but it doesn’t seem to be, even if the black mesh is disposed of (which I’d prefer not to do).

The red mesh is definitely present and, if created first, displays properly.