I should point out that 3Dstudio R3 ( .3DS files are the files that it used ) could not deal with unwrapped maps ( it's like 15 years old... ). It was either planar, cylindrical or spherical. And nothing else. When you convert your mesh to 3ds, you have to remember that limitation. So what happens? During the conversion process, all the polys that don't follow the above rule are separated from the mesh, creating as many planar mapped objects as needed. In Max terms, that means that all those polys are turned into elements, and have their own edges, not shared with the neighbour polygon.
That means you have to weld the vertices back when you're opening it with your program ( AfaIk, TS can't, but you can weld the verts in 3Dexploration ).