minecart not moving until I follow it

I made a rail system that takes a minecart with a chest from A to B. It loads stuff to the cart from a chest at A and is then supposed to go to B to unload in a chest there, return and repeat. What happens is the cart starts moving and goes out of sight but never returns. So I go and check on it and when I get to the point where I last saw it, it starts moving again. It's like it just pauses when it goes out of sight of the player. Everything works fine if I just fallow the cart all the way from A to B and back but that really defeats the purpose of the rail system.

Length between the A and B is somewhere between 500 and 1000m I think(blocks) I can't be sure because we don't have the F3 function in this version to show the coordinates.