Alphamaps with new cloned terrain

I am tiling terrains together. It works well for the height maps, all my tiles are properly showing their own relief. Where things go weird is when setting the alpha maps of the new tiles.

I am making sure to clone the TerrainData from my template tile

         TerrainData data = UnityEngine.Object.Instantiate(template.terrainData) as TerrainData;
         GameObject terrainObject = Terrain.CreateTerrainGameObject(data);
         Terrain result = terrainObject.GetComponent<Terrain>();

If I set the alpha maps on result, it sets it for all the terrains in my scene, including the template. So obviously something isn't cloned corectly, but I have no idea where.

To set the alpha map, all I do is:

         float[,,] map = new float[result.terrainData.alphamapWidth, 
                     result.terrainData.alphamapHeight, 
                     result.terrainData.alphamapLayers];

then after filling the map values:

         result.terrainData.SetAlphamaps(0, 0, map);

I have no idea what I'm doing wrong