RadGrid HeaderContext filter menu throws '_linkElement' undefined error after expand animation ends in version 2026.1.211.462

After clicking the filter icon in a RadGrid column header, the filter menu throws the following JavaScript error in the browser console:

Uncaught TypeError: Cannot read properties of undefined (reading '_linkElement')
    at Object._focusFirstItem
    at Object.raise_expandAnimationEnded
    at Object._onExpandAnimationEnded

Environment:
- Telerik UI for ASP.NET AJAX version: 2026.1.211.462
- ASP.NET Framework: 4.8.1
- Browser: Chrome (latest)
- FilterType: default
- RadScriptManager with no custom script references

Steps to reproduce:
1. Place a RadGrid with AllowFilteringByColumn="true"
2. Run the application
3. Click the filter icon on any column header
4. Observe the JavaScript error in the browser console after the menu animation completes

Expected behavior:
The filter menu opens and focus is set on the first menu item without any errors.

Actual behavior:

The filter menu disappears visually, does not appear, and throws a JS exception when attempting to focus the first item (_linkElement is undefined)

I have updated my project to the latest version 2026.1.211.462 but when I add the speechtotextbutton, I get failed to create designer telerik.web.ui.radspeechtotextbutton

After upgrading to Telerik UI for ASP.NET AJAX 2026 Q1 (2026.1.211.462) the HtmlChart Sparkline cannot initialize.

The demo page loads, but the chart is empty and the component is not usable.

The browser console shows a JavaScript initialization failure originating from the Telerik scripts.

The first error thrown is:

Uncaught ReferenceError: kendo is not defined
    at Telerik.Web.UI.WebResource.axd...

Immediately after that a second error appears:

Uncaught TypeError: kendo.jQuery(...).kendoSparkline is not a function

The second error is a cascade failure because the Kendo widgets are never registered due to the first error.

We have a WebForms application with Telerik AJAX components which we have successfully upgraded using the wizard for years. Starting with product version 2025.4.1210 and persisting in the latest version, 2025.4.1321, the upgrade wizard fails with the following error message.

The Telerik extension to VS is up to date, and it doesn't seem to help to run this in VS 2022.

An error occurred while running the wizard.

Error executing custom action Telerik.Web.UI.VSX.Actions.MultiProjectUpdateReferencesAction: System.InvalidOperationException: There is an error in XML document (3, 2). ---> System.Xml.XmlException: Name cannot begin with the '<' character, hexadecimal value 0x3C. Line 3, position 2.
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.ParseQName(Boolean isQName, Int32 startOffset, Int32& colonPos)
   at System.Xml.XmlTextReaderImpl.ParseElement()
   at System.Xml.XmlTextReaderImpl.ParseElementContent()
   at System.Xml.XmlReader.ReadStartElement()
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderSolutionDistributionDefinition.Read2_SolutionDistributionDefinition(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderSolutionDistributionDefinition.Read3_Distribution()
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
   at System.Xml.Serialization.XmlSerializer.Deserialize(TextReader textReader)
   at Telerik.VSX.Helpers.Serializer`1.Deserialize(String filePath)
   at Telerik.VSX.SolutionManagement.SolutionDistributionOperator.<>c__DisplayClass11_0.<DeserializeSolutionDistributionDefinition>b__0()
   at Telerik.VSX.SolutionManagement.SolutionDistributionOperator.HandleUnauthorizedAccessException(Action action)
   at Telerik.VSX.SolutionManagement.SolutionDistributionOperator.DeserializeSolutionDistributionDefinition(String distributionFilePath)
   at Telerik.VSX.SolutionManagement.SolutionDistributionOperator.<>c__DisplayClass10_0.<CreateSolutionDistribution>b__0()
   at Telerik.VSX.SolutionManagement.SolutionDistributionOperator.HandleUnauthorizedAccessException(Action action)
   at Telerik.VSX.SolutionManagement.SolutionDistributionOperator.CreateSolutionDistribution(String distributionFilePath, DistributionInfo distributionInfo)
   at Telerik.VSX.SolutionManagement.SolutionDistributionsContext.LoadSolutionDistributionDefinitions(DistributionInfo distributionInfo)
   at Telerik.VSX.Actions.MultiProjectUpdateReferencesActionBase`1.CreateSolutionDistributionsContext(WizardContext context)
   at Telerik.VSX.Actions.MultiProjectUpdateReferencesActionBase`1.Execute(WizardContext wizardContext, IPropertyDataDictionary arguments)
   at Telerik.VSX.WizardEngine.ActionManager.ExecActions()

Hello Telerik Team,

I'm implementing HeaderContext filtering with checkbox lists on a RadGrid in a legacy ASP.NET WebForms application. 

Current Setup:
- FilterType="HeaderContext"
- FilterCheckListEnableLoadOnDemand="true"
- OnFilterCheckListItemsRequested event populates checkboxes from session data

Issue:
Users experience 500-2000ms delay when opening filter menus (AJAX callback to server). 
In our production environment with slow network and high concurrent users, this creates 
poor user experience.

Questions:
1. Is there a way to pre-populate checkbox lists during grid initialization 
   (avoiding AJAX callback)?
2. Can we use OnItemCreated to populate checkbox lists with 
   FilterCheckListEnableLoadOnDemand="false"? If so, what's the correct approach?
3. Is there a client-side caching mechanism for checkbox list items?
4. What's the recommended pattern for large datasets (1000+ rows) with multiple 
   filterable columns?

Environment:
- Telerik.Web.UI version: v4.0.30319
- .NET Framework: 4.8
- Browser: Chrome, IE11
- Grid has ~10 columns with 5 using checkbox filters

Any guidance on performance optimization would be greatly appreciated!

Thank you,
Anurag pandey

The gantt throws Uncaught ReferenceError: kendo is not defined when clicking on the calendar picker button.

The spreadsheet throws Uncaught ReferenceError: kendo is not defined when you type in a number in the quantity field, then click to the next cell.

For a better description of the issue and reproduction steps, please view the ticket:

http://www.telerik.com/account/support-tickets/view-ticket?threadid=1010438

If a user clicks 'Ignore All' for a misspelled word, the focus moves to the next misspelled word after the last word included in the ignore all list.  This becomes problematic when editing a large quantity of text and the user's trying to go through things in order, but the focus moves to the very bottom of the content area.

In MS Word, it works as our users expect it would.  Once 'Ignore All' is chosen, the very next misspelled word is highlighted.

The tabs get hidden when a top oriented SlidingPane is docked inside a horizontal SlidingZone. The issue is reproducible when the resize mode of the parent Splitter is != AdjacentPane.

Steps to reproduce:
1. Run the following code:

        <div style="padding: 200px">
            <telerik:RadSplitter runat="server" ID="RadSplitter2" Orientation="Horizontal" ResizeMode="Proportional">
                <telerik:RadPane runat="Server" ID="radpane11" Height="20px" MaxWidth="980" Scrolling="None" BackColor="Green">
                    <telerik:RadSlidingZone ID="ListMetricsSlidingZone" runat="server" Height="25px" DockedPaneId="ListMetricsPane" SlideDirection="Top">
                        <telerik:RadSlidingPane ID="ListMetricsPane" Title="DEF" runat="server">
                            1111
                        </telerik:RadSlidingPane>
                        <telerik:RadSlidingPane ID="ListHistorySlidingPane1" Title="XYZ" Font-Size="X-Large" runat="server">
                            222
                        </telerik:RadSlidingPane>
                    </telerik:RadSlidingZone>
                </telerik:RadPane>
                <telerik:RadPane runat="Server" ID="radpane33" Scrolling="None">
                </telerik:RadPane>
            </telerik:RadSplitter>
        </div>

2. Undock and dock a sliding pane.

Expected: The tabs remains visible all the time (change the Splitters ResizeMode="AdjacentPane" for reference)

The MaxFileSize property is an int - this means a limit over 2GB can't be set. Please change this property to a long.