stringstretcher,
that happens if you're twisting one bundle around the other, rather than reverse twisting the two of them together. Kind of hard to explain, but the extreme of it would be to think of it like winding a cord around a stick.
I don't use a board. After making a few strings out of a given material you get a feel for how much it stretches and settles in. My first dacron string ended up being an inch too long b/c I made it like I had been making the TS-1 strings. Does the board adjust for string material?