The issue happens with RenderMode Lightweight, under IE, when the panel bar is in a scrolled container.
Workarounds:
- use the Classic Render Mode
- store the container scroll position when the item expands, restore it after animation ends, by using the control events. Sample is attached below. Note that you need to find the actual container that scrolls, and this will vary with every different layout of your real page.

You should, in general, use the ContentTemplate to provide content to items.

By original design and old documentation, the ItemTemplate must not be collapsible at all, but since it has been for ages, we must fix that to avoid a breaking change.

Items that have an ItemTemplate have the following collapse/expand issues:

    - they require two clicks to collapse for the first time
    - setting Expanded=false on the server keeps the ItemTemplate expanded
    - until you click their header they do not heave the coloring and expand/collapse arrow

See this changeset on how the templates should work and the change from the previous descriptions: https://github.com/telerik/ajax-docs/commit/67f0a252ff24e2397e042fe5797de3610a75221d which is available in the following article http://docs.telerik.com/devtools/aspnet-ajax/controls/panelbar/templates/overview

When tabbing from first PanelBar to the second one it neither passes through the contentTemplate elements, nor to the second panelbar:
 
<telerik:RadPanelBar runat="server" ID="radPnlBarFundingSources" Width="100%" ExpandMode="MultipleExpandedItems" TabIndex="1">
            <Items>
                <telerik:RadPanelItem runat="server" Text="Funding Source">
                    <ContentTemplate>
                        <telerik:RadListBox runat="server" ID="radLbAvailFundingSource" Height="100px" Width="40%" SelectionMode="Multiple" AllowTransfer="true" TransferMode="Move" AllowTransferOnDoubleClick="true" TransferToID="radLbSelFundingSource" ButtonSettings-AreaWidth="35px" Enabled="True" style="font-family: Verdana, Trebuchet MS,Arial,sans-serif; font-size:0.9em;"></telerik:RadListBox>
                        <telerik:RadListBox runat="server" ID="radLbSelFundingSource" Height="100px" Width="40%"></telerik:RadListBox>
                    </ContentTemplate>
                </telerik:RadPanelItem>
            </Items>
        </telerik:RadPanelBar>
    </div>
    <div class="Row">
        <telerik:RadPanelBar runat="server" ID="radPnlBarContracts" Width="100%" TabIndex="2">
            <Items>
                 <telerik:RadPanelItem runat="server" Text="Contract">
                    <ContentTemplate>
                        <telerik:RadListBox runat="server" ID="radLbAvailContract" Height="100px" Width="40%" SelectionMode="Multiple" AllowTransfer="true" AllowTransferOnDoubleClick="true" TransferToID="radLbSelContract"  AutButtonSettings-AreaWidth="35px"></telerik:RadListBox>
                        <telerik:RadListBox runat="server" ID="radLbSelContract" Height="100px" Width="40%"></telerik:RadListBox>
                    </ContentTemplate>
                 </telerik:RadPanelItem>
            </Items>
        </telerik:RadPanelBar>

The panelbar item you click on selects the first root item of the panelbar, then changes to the actual selected item. This can be observed in the Custom Attributes demo.

------------------- AI Summary -------------------

We upgraded Telerik UI for ASP.NET AJAX from version 2026.2.708 to 2026.3.812, with no changes to our navigation menu code. Our RadPanelBar menu is populated server-side via DataBind() using a SiteMapDataSource (no client-side population). Since the upgrade, clicking a menu item frequently does not navigate to its URL: the menu shifts vertically, the clicked item is not selected, and no navigation occurs. This is impacting customers’ ability to use our site.

--------------- End of AI Summary ---------------

We are requesting assistance to troubleshoot and resolve this issue as quickly as possible. This problem is causing significant usability issues.