I think something like this was reported a while back, but it’s still occurring with any form of mesh (including meshes rendered via SpecialMesh) and I haven’t found any topics about this particular bug. If you apply a mesh texture or Decal to any mesh, the raw mesh shape will remain opaque and neon unless you set the Transparency to anything except zero.
A grass mesh with 0.000 Transparency
Same grass mesh with 0.001 Transparency
I know the universal workaround is, as exemplified - to set the Transparency to 0.001, but it would be most preferable if this was fixed whenever possible.