Quite all CSS transitions are working smoothly, but it’s not the case of a transition of a “margin” property. You can test it for example with the following code in a Widget Factory, but I had initially the problem with a “modelbutton” node (and it’s tested either with “linear” or “ease”).

  button.toggle {
    margin:0px 5px;
    transition:margin 2s linear 0s;
  }
  button.toggle:hover {
    margin:0px;
  }

I’d say the problem is that the transition is calculated pixel by pixel but with one more step than really needed, so it’s waiting twice at the start or end step (depending of “ease” or “linear”) of the transition.