Undoing last point when drawing linestring in OpenLayers 3?

I would like to be able to draw a linestring and to be able to undo the last drawn point when the key ESC is pressed.

I used that code when I first wrote my application :

  // create the interaction

  draw_interaction = new ol.interaction.Draw({
    source: vector_layer.getSource(),
    type: /** @type {ol.geom.GeometryType} */ ($geom_type.val())
  });
    // add it to the map
  map.addInteraction(draw_interaction);

  // when a new feature has been drawn...
  draw_interaction.on('drawstart', function(evt) {
    var feature = evt.feature;

    var geom = feature.getGeometry();
    document.addEventListener('keyup', function() {
      if (event.keyCode === 27) {
        if (geom.getType() === "LineString") {
          var coords = geom.getCoordinates();
          var len = coords.length;
          console.log("undo");
          if (len > 1) {
           geom.setCoordinates(geom.getCoordinates().slice(0, len - 1));
          }

        }
      }
    });
  });

You can see a live version on codepen following that link:

http://codepen.io/anon/pen/waPXyG

My problem is when I upgraded from 3.5.0 to 3.6.0, the behaviour changed :

http://codepen.io/anon/pen/LVOrrq

As you can see on the live example, when undoing (pressing ESC) it seems to be working but when you want to add a new point to the linestring, the points I removed are back in place. Looks like a caching behaviour as been added to 3.6.0

I hope someone can help me, it's either a regression or a api modification that I did not notice in the change log.

Answer

Since OpenLayers 3.9.0, this is as simple as using the removeLastPoint method of the DrawInteraction. So you can do something like this:

document.addEventListener('keydown', function(e) {
    if (e.which == 27)
        draw_interaction.removeLastPoint()
});