[Multitexture terrain] glowing artifacts in the transition

Hello, i'm having a strange issue that happens only when ambient light is dark and only for the 5th, 6th terrain texture
I also tried to change the texture without success.
Have you an idea where i can investigate to find the bug?

Related: http://answers.unity3d.com/questions/595067/blending-edges-of-textures-in-the-terrain-editor.html



black ambient light with 0 intensity