Hello,

We have reviewed the case further, and we've found another workaround which should work in all cases. It involves overriding a single method of RadTreeViewElement, but you also need to create a derived class of RadTreeView in order to plug the custom element:

        public class MyTreeViewElement : RadTreeViewElement
        {
            protected override void UpdateScrollersOnNodesNeeded(RadTreeNode node)
            {
                var nodesField = node.GetType().GetField("nodes", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
                RadTreeNodeCollection nodes = nodesField.GetValue(node) as RadTreeNodeCollection;
                if (nodes != null && nodes.Count > 0)
                {
                    base.UpdateScrollersOnNodesNeeded(node);
                }
            }

            protected override Type ThemeEffectiveType
            {
                get
                {
                    return typeof(RadTreeViewElement);
                }
            }
        }

        public class MyTreeView : RadTreeView
        {
            protected override RadTreeViewElement CreateTreeViewElement()
            {
                return new MyTreeViewElement();
            }

            public override string ThemeClassName
            {
                get
                {
                    return typeof(RadTreeView).FullName;
                }
                set
                {
                    base.ThemeClassName = value;
                }
            }
        }

After you have this, you need to go through your Designer files and replace "new Telerik.WinControls.UI.RadTreeView();" with "new MyTreeView()";

We do understand the importance of this case, however, for the time being, we do not plan releasing an internal build for it, as adopting the workaround is easier than working with an internal build. However, depending on the reports, we might consider releasing an internal build in future. For now, the issue is scheduled for the next official release.