what is the difference between eventstream zip and Bacon.when

Question

I thought these were supposed to be equivalent but they are not:

  // wrong
  // let esDragStackCancelWithCards =
  //     esDragStackCancel.zip(esDragCardsEarly, fMergeArgs);

  let esDragStackCancelWithCards =
      Bacon.when(
        [esDragStackCancel, esDragCardsEarly, fMergeArgs]);

I get the correct behaviour on Bacon.when, and wrong behaviour on zip. The behaviour is about drag drop of cards. I want to sample esDragCardsEarly when esDragStackCancel happens.

Also I don't want buffering to happen how do I test for that?