Pistons stop moving outside world border

I'm not sure if this is a bug or not, but if it isn't, its rather annoying. I have a spawn pad set at the co-ordinates of (1500,0) and when the first player steps into the spawn pad, it sets off a list of command blocks, including Worldborder (center = 0,0 and length of blocks = 1000). My concern is that, I have a few pistons inside the machine, that work at first, but as soon as the world border is set into effect, it stops due to it being outside the world border. Let me know if this is intended or a bug.
Thanks!