Terrain Texture Glossy Edge at Intersection

Using the Terrain component I have 9 textures/splats. When certain textures intersect they have a glossy edge (textures 4, 5, 7, and 8). See below.

Even though splat8 and splat9 are identical (same albedo, no normal, same tiling, same offset) only splat8 has the glossy edge!

What I've noticed:
1: If I change the Terrain shader from "Built in Standard" to "Legacy Diffuse" the problem goes away (but Legacy Diffuse has no shadows so I can't use it)
2: If I start from scratch and rebuild the terrain the issue is repeatable (splats 4, 5, 7 and 8)
3: Only certain textures have this issue... in certain slots. Examples:
Grass0 as splat1: OK
Cobble2 as splat1: OK
Grass0 as splat8: OK
Cobble0 as splat8: Glossy edge
Cobble1 as splat8: Glossy edge
Cobble2 as splat8: Glossy edge
Cobble0 as splat9: OK
Cobble1 as splat9: OK
Cobble2 as splat9: OK
4: All this occurs with no normal maps on all textures. If I add in the normal maps then the smooth glossy edge turns into pixelated white dots. (on splats 4, 5, 7, and 8)

Is this a bug (should I bug report?). Any ideas for things to try would be appreciated.

 

SOLUTION: Change the import settings of the textures to AlphaSource: None
Reason: It seems the alpha channel is used for shininess/metalness/reflectivity/smoothness or something?

I still have no idea why 2 splats using the same texture with all the same settings behave differently... this still appears like a bug.

 

Bug reported case #894053