@dave1707 The way the icosphere is set up, in the non-smooth case then every position is in a unique triangle. This leads to vertices being duplicated quite a lot (roughly five or six times) but this is needed because although the positions are the same for each re-use of the vertex, other data (specifically the normals) is not.
However, in the smooth case, the normals depend only on the vertex and not on the triangle and therefore the vertices can be re-used in different triangles. For the vast majority of the vertices, this is okay with the texture as the texture coordinates only depend on the position on the sphere.
Where this fails is at the edges of the texture, which with the usual sphere wrapping are at the poles and at the seam. At these places, more than one point on the texture goes to the same point on the sphere. This is perhaps most obvious at the poles where the entire top of the texture maps to the north pole (and bottom to the south pole). Therefore, the texture coordinate at the north pole depends on which triangle is under consideration. So the pole needs duplicating, once for each triangle it is in. A similar thing happens down the seam.