I just had a problem with when.js + jquery's deferreds.

when.map(someBackboneModels, function (model) {
  return model.save(); // this returns a jquery's ajax result
}).then(
  function () {
    console.log('success');
  },
  function () {
    console.log('error');
  }
);

In case of success, everything works as expected. In case of the error, when.js starts calling it's internal functions recursively and kills the browser..

I will try to reproduce/identify the problem, but do you spot anything wrong with the above?