Node.js This Fiber is already running

Question

I have a question regarding usage of Fibers in Node.js. The following code fails with error message:

This Fiber is already running

on train routine.

var f = Fiber(function() {
  var fiber = Fiber.current;

  utils.enseeds(seeds, function(err, response){
    fiber.run(response)
  })

  var myseeds = Fiber.yield()

  utils.train(train, test, myseeds, function(err, response){
    fiber.run(response)
  })

  var stats = Fiber.yield()
})

f.run();

For some reason it doesn't like myseeds, if I change myseeds in train to something else it works. Why does this happen?