diff --git a/src/DataSet.js b/src/DataSet.js
index 40c16504..de6f5c09 100644
--- a/src/DataSet.js
+++ b/src/DataSet.js
@@ -47,6 +47,7 @@ function DataSet (data, options) {
 
   this.options = options || {};
   this.data = {};                                 // map with data indexed by id
+  this.length = 0;                                // number of items in the dataset
   this.fieldId = this.options.fieldId || 'id';    // name of the field containing id
   this.convert = {};                              // field types by field name
   this.showInternalIds = this.options.showInternalIds || false; // show internal ids with the get function
@@ -685,6 +686,7 @@ DataSet.prototype._remove = function (id) {
     if (this.data[id]) {
       delete this.data[id];
       delete this.internalIds[id];
+      this.length--;
       return id;
     }
   }
@@ -693,6 +695,7 @@ DataSet.prototype._remove = function (id) {
     if (itemId && this.data[itemId]) {
       delete this.data[itemId];
       delete this.internalIds[itemId];
+      this.length--;
       return itemId;
     }
   }
@@ -709,6 +712,7 @@ DataSet.prototype.clear = function (senderId) {
 
   this.data = {};
   this.internalIds = {};
+  this.length--;
 
   this._trigger('remove', {items: ids}, senderId);
 
@@ -828,6 +832,7 @@ DataSet.prototype._addItem = function (item) {
     }
   }
   this.data[id] = d;
+  this.length++;
 
   return id;
 };
diff --git a/src/timeline/Timeline.js b/src/timeline/Timeline.js
index ca24de0b..8edadcac 100644
--- a/src/timeline/Timeline.js
+++ b/src/timeline/Timeline.js
@@ -497,6 +497,7 @@ Timeline.prototype.getWindow = function() {
  */
 Timeline.prototype.redraw = function() {
   var resized = false,
+      updateProperty = util.updateProperty,
       options = this.options,
       props = this.props,
       dom = this.dom;
@@ -519,12 +520,15 @@ Timeline.prototype.redraw = function() {
 
   // calculate the heights. If any of the side panels is empty, we set the height to
   // minus the border width, such that the border will be invisible
-  props.center.height = dom.center.offsetHeight;
+  //props.center.height = dom.center.offsetHeight;
+  resized = updateProperty(props.center, 'height', this.itemSet.props.height || 0) || resized; // TODO: this is a really ugly hack
   props.left.height   = dom.left.offsetHeight;
   props.right.height  = dom.right.offsetHeight;
   props.top.height    = dom.top.clientHeight    || -props.border.top;
   props.bottom.height = dom.bottom.clientHeight || -props.border.bottom;
 
+  console.log('props.center.height', props.center.height);
+
   // TODO: compensate borders when any of the panels is empty.
 
   // apply auto height
@@ -532,7 +536,7 @@ Timeline.prototype.redraw = function() {
   var contentHeight = Math.max(props.left.height, props.center.height, props.right.height);
   var autoHeight = props.top.height + contentHeight + props.bottom.height +
       borderRootHeight + props.border.top + props.border.bottom;
-  dom.root.style.height = util.option.asSize(options.height, autoHeight + 'px');
+  resized = updateProperty(dom.root.style, 'height', util.option.asSize(options.height, autoHeight + 'px')) || resized;
 
   // calculate heights of the content panels
   props.root.height = dom.root.offsetHeight;
@@ -679,8 +683,10 @@ Timeline.prototype._startAutoResize = function () {
   this._stopAutoResize();
 
   function checkSize() {
-    if (me.options.autoResize != true) {
-      // stop watching when the option autoResize is changed to false
+    if (me.options.autoResize != true || !me.dom.root.parentNode) {
+    //if (me.options.autoResize != true) {
+      // stop watching when the option autoResize is changed to false,
+      // or when the Timeline is no longer attached to the DOM.
       me._stopAutoResize();
       return;
     }
@@ -697,7 +703,6 @@ Timeline.prototype._startAutoResize = function () {
     }
   }
 
-  // TODO: automatically cleanup the event listener when the frame is deleted
   util.addEventListener(window, 'resize', checkSize);
 
   this.watchTimer = setInterval(checkSize, 1000);
diff --git a/src/timeline/component/Group.js b/src/timeline/component/Group.js
index 343ba185..b67d12e9 100644
--- a/src/timeline/component/Group.js
+++ b/src/timeline/component/Group.js
@@ -78,6 +78,7 @@ Group.prototype.setData = function(data) {
     this.dom.inner.innerHTML = this.groupId;
   }
 
+  // Mark hidden when empty
   if (!this.dom.inner.firstChild) {
     util.addClassName(this.dom.inner, 'hidden');
   }
@@ -89,18 +90,11 @@ Group.prototype.setData = function(data) {
   var className = data && data.className;
   if (className) {
     util.addClassName(this.dom.label, className);
+    // TODO: addClassName to contents as well
   }
+  // TODO: be able to remove className
 };
 
-/**
- * Get the width of the group label
- * @return {number} width
- */
-Group.prototype.getLabelWidth = function() {
-  return this.props.label.width;
-};
-
-
 /**
  * Repaint this group
  * @param {{start: number, end: number}} range
@@ -154,7 +148,7 @@ Group.prototype.redraw = function(range, margin, restack) {
 
   // calculate actual size and position
   var foreground = this.dom.foreground;
-  this.top = foreground.offsetTop;
+  this.top = this.itemSet.getGroupTop(this.groupId); // top is determined by the ItemSet, from the heights of previous groups
   this.left = foreground.offsetLeft;
   this.width = foreground.offsetWidth;
   resized = util.updateProperty(this, 'height', height) || resized;
diff --git a/src/timeline/component/ItemSet.js b/src/timeline/component/ItemSet.js
index 95c5ed86..be01dac8 100644
--- a/src/timeline/component/ItemSet.js
+++ b/src/timeline/component/ItemSet.js
@@ -385,7 +385,8 @@ ItemSet.prototype._deselect = function(id) {
  * @return {boolean} Returns true if the component is resized
  */
 ItemSet.prototype.redraw = function() {
-  var margin = this.options.margin,
+  var me = this,
+      margin = this.options.margin,
       range = this.body.range,
       asSize = util.option.asSize,
       options = this.options,
@@ -421,7 +422,8 @@ ItemSet.prototype.redraw = function() {
       },
       height = 0,
       minHeight = margin.axis + margin.item;
-  util.forEach(this.groups, function (group) {
+  this.groupIds.forEach(function (groupId) {
+    var group = me.groups[groupId];
     var groupMargin = (group == firstGroup) ? firstMargin : nonFirstMargin;
     var groupResized = group.redraw(range, groupMargin, restack);
     resized = groupResized || resized;
@@ -451,6 +453,24 @@ ItemSet.prototype.redraw = function() {
   return resized;
 };
 
+/**
+ * Calculate the top for a group
+ * @param {Number} groupId
+ */
+ItemSet.prototype.getGroupTop = function(groupId) {
+  var top = 0,
+      count = this.groupIds.length,
+      orientation = this.options.orientation;
+  for (var index = 0; index < count; index++) {
+    var id = this.groupIds[index];
+    if (id == groupId) break;
+
+    top += this.groups[id].height;
+  }
+
+  return top;
+};
+
 /**
  * Get the first group, aligned with the axis
  * @return {Group | null} firstGroup
diff --git a/src/timeline/component/css/animation.css b/src/timeline/component/css/animation.css
index 0b03f57f..3ea58b18 100644
--- a/src/timeline/component/css/animation.css
+++ b/src/timeline/component/css/animation.css
@@ -1,26 +1,23 @@
-.vis.timeline.root {
-  /*
-  -webkit-transition: height .4s ease-in-out;
-  transition:         height .4s ease-in-out;
-  */
-}
-
-.vis.timeline .vispanel {
-  /*
+/*
+  Note: .vis.timeline.root may not have transitions, else its height cannot be
+  determined (depends on autoHeight, css height, css minHeight, and css maxHeight)
+*/
+/*.vis.timeline.root,*/
+.vis.timeline .axis,
+.vis.timeline .vispanel.center,
+.vis.timeline .vispanel.left,
+.vis.timeline .vispanel.right,
+.vis.timeline .vispanel.bottom {
   -webkit-transition: height .4s ease-in-out, top .4s ease-in-out;
   transition:         height .4s ease-in-out, top .4s ease-in-out;
-  */
 }
 
-.vis.timeline .axis {
-  /*
-  -webkit-transition: top .4s ease-in-out;
-  transition:         top .4s ease-in-out;
-  */
+.vis.timeline .vispanel .itemset .group,
+.vis.timeline .vispanel .labelset .vlabel {
+  -webkit-transition: height .4s ease-in-out;
+  transition:         height .4s ease-in-out;
 }
 
-/* TODO: get animation working nicely
-
 .vis.timeline .item {
   -webkit-transition: top .4s ease-in-out;
   transition:         top .4s ease-in-out;
@@ -30,4 +27,3 @@
   -webkit-transition: height .4s ease-in-out, top .4s ease-in-out;
   transition:         height .4s ease-in-out, top .4s ease-in-out;
 }
-/**/
\ No newline at end of file
diff --git a/test/timeline_groups.html b/test/timeline_groups.html
index de2f5b16..4e0c11b1 100644
--- a/test/timeline_groups.html
+++ b/test/timeline_groups.html
@@ -79,6 +79,7 @@
       updateTime: true,
       updateGroup: true
     },
+    autoResize: false,
     //stack: false,
     //height: 200,
     groupOrder: 'content'