src/map/Map.js
function (group) {
    var map = this;

    if (group.eachLayer) {
      group.eachLayer(function (layer) {
        map._updateAllLayers(layer);
      });
    } else {
      if (group.redraw) {
        group.redraw();
      } else if (group.update) {
        group.update();
      } else {
        console.log("Don't know how to update", group);
      }
    }
  }
function (group) {
    var map = this;

    if (group.eachLayer) {
      group.eachLayer(function (layer) {
        map._updateAllLayers(layer);
      });
    } else {
      if (group.redraw) {
        group.redraw();
      } else if (group.update) {
        group.update();
      } else {
        console.log("Don't know how to update", group);
      }
    }
  }
This recurses through all the map's layers to update layer positions after their positions moved.