Just to test this and find a way to fix this i made a plane divided into 4 faces with 4 different materials.. each face has the same seamless material on it with a baked light ontop of the whole plane.. all textures look perfectly fine in Photoshop.. 1024x1024 8bit .tga images.. once uploaded into sl where the seam lines are there are weird lines.. I use Maya and bake textures using UDIMs with vray render engine.
Screenshot from Secondlife:
Screenshot from the same seam lines in Photoshop:
UV's in Maya