Terrain texture artifacts when normal mapped

I am experiencing a strange issue with some textures on my terrain (it does not happen to all). When lined up next to another texture, a strange artifact will appear along the two. Both have normal maps, are the same size etc. so I am not sure what the issue is.

Attatched is an image of this artifact. It occurs around the dirt/grass texture, yet the various other grass textures are fine.


TerrBumpAddPass Replacement Shader:

I made a replacement shader to help me overcome this problem (at least on Windows desktop, I suspect it won’t work well on some devices). It can blend over 8 textures.

Details, screenshot comparison and download link (it’s free of course) all available at the following URL: