How do I get Normal Maps to align with Tile Maps?

In this image I have 3 sprites: Rock, Grass and Dirt.

The Rock is 32x32 and Grass is 16x16. They are single sprites each with their own normal map. The Dirt is from a tilemap 144x144 and the normal map is also 144x144. The Dirt tilemap is sliced into 9 rows/columns creating several 16x16 tiles.

The normal maps appear perfectly aligned with the Rock and Grass but for some reason they are out of alignment with the Dirt. I have not manually sliced the normal map but have relied on Unity using the same UV co-ordinates as in the tile map.

I'm using the standard shader and have tried this in Unity 5.3.2f1 and 5.4 and both give the same result.