Repro steps:
1) Open DrawMeshNow project I attached and asd.scene
2) Notice three objects(1st drawn with DrawMesh(), 2nd - DrawMeshNow, 3rd- simple gameobject)
3) Notice that part of front(lamps in white) is missing in the 1st object
but not in the second, as only one submesh was drawn
4) Open DrawMesh.cs and look at OnDrawGizmos
5) Notice that DrawMeshNow().materialIndex is the same as DrawMesh().submeshIndex
6) According to docs:
(DrawMesh)submeshIndex Which subset of the mesh to draw
(DrawMeshNow)materialIndex Subset of the mesh to draw.

Expected: DrawMeshNow().materialIndex should work the same as submeshIndex, as written in docs
Actual: All submeshes are being drawn

Reproduced in: 5.4.0b7; 5.3.3f1; 5.2.3p3