Consider the use of TextWriter async methods for the HTML Helpers, for example the WriteInitializationScript methods.  In certain scenarios the use of the synchronous methods causes an exception: System.InvalidOperationException: Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.

This can be resolved by explicitly enabling synchronous operations

services.Configure<IISServerOptions>(options =>
    {
        options.AllowSynchronousIO = true;
    });

though synchronous operations have been disabled by default at framework level as of .NET 3.0.

Bug report

Reproduction of the problem

1. Open the Dojo - https://dojo.telerik.com/FcHfotEy
2. Hover over more than one image

Current behavior

Only the first image has the correct width and height

Expected/desired behavior

The Tooltip should respect the width and height size configurations.

Workaround:

contentLoad: function (e) {
              $(".k-tooltip.k-popup").width(500).height(500);
            },

https://dojo.telerik.com/lvXLxxYD 

TicketID: 1717434

The issue is a regression starting with 2026.2.520 version

Environment

• Kendo/Telerik version: 2026.2.520
• Browser: [all ]

Bug report

The DateTimePicker's popup calendar view is cut in the Default, Classic, and Fluent themes.

Reproduction of the problem

1. Run the following dojo
2. Set the sizing option of the widget to large.
3. Open to DatePicker popup.

Current behavior

The Date and Time views in the DateTimePicker popup are trimmed.

Expected/desired behavior

The Date and Time views in the DateTimePicker popup should not be trimmed.

Environment

• Kendo UI version: 2023.1.117
• Browser: [all]

### Bug report

When subscribing to the "requestStart"/"requestEnd" events of the DataSource after the Grid's initialization, the events do not fire during the Excel export.

### Reproduction of the problem

1. Enable the server operations of the Grid's DataSource.

2. Get a reference to the Grid and handle the DataSource "requestStart"/"requestEnd" events by using the bind() method.

3. Export the Grid's data to Excel through the built-in command.

4. The "requestStart"/"requestEnd" events do not trigger when the read request is activated.

A Dojo sample for reproduction: https://dojo.telerik.com/eyiDIGeM

### Expected/desired behavior

The  "requestStart"/"requestEnd" events must trigger when exporting the Grid to Excel.

### Environment

* **Kendo UI version: 2024.3.806
* **jQuery version: 3.7.0
* **Browser: all

### Bug report

When adding custom classes or styles to the TimeDurationPicker component, they are applied to the hidden input elenent rather than to the parent element.

### Reproduction of the problem

1. Create a TimeDurationPicker and add a class to its element:

<input id="timedurationpicker" class="testClass" />

2. When you inspect the component's markup, the "testClass" is added to the hidden input element.

A Dojo sample for reproduction: https://dojo.telerik.com/IsTnGqsk

### Expected/desired behavior

Any custom attributes must be added to the parent element with class "k-timedurationpicker".

### Environment

* **Kendo UI version: 2025.2.520
* **jQuery version: 3.7.1
* **Browser: [all]

Bug report

Even if a message file is added, the command buttons and the popup title in the Grid are not localized

Reproduction of the problem

1. Open the Dojo examples:

• Dojo with messages file - https://dojo.telerik.com/CehWjRrE
• Dojo with overriding the kendo.ui.Grid.prototype.options.messages - https://dojo.telerik.com/RWCxqxIm

2. Decrease the size of the screen so the Grid to be displayed in adaptive mode.
3. Click on a row and select the 'Edit' button to open the Edit popup

Current behavior

The command buttons and the dialog title are not localized:

Expected/desired behavior

It should be possible to change and localize the messages texts.

Workaround

 function onEdit(e){
      e.container.closest('.k-window').find('.k-window-title').text('My custom text')
      e.container.closest('.k-window').find('.k-button[ref-update-button]').text('Button Update Changed');
      e.container.closest('.k-window').find('.k-button[ref-cancel-button]').text('Button Cancel Changed');
 }

Environment

• Kendo UI version: 2025.4.1217
• Browser: [all ]

Product:

Telerik UI for ASP.NET Core (Grid)
Component: Grid Popup Editing
Version: 2026.2.520

Description:

I am experiencing an inconsistent focus behavior when using a Kendo Grid configured with Popup Editing.
After opening the popup editor and closing it using the Window close button (X), a Grid cell remains visually focused. The focused cell contains the CSS class k-focus.
The visual outline disappears immediately if the k-focus class is manually removed:

$(".k-focus").removeClass("k-focus");

However, removing the browser focus with:

document.activeElement?.blur();

does not remove the visual outline, which suggests that the issue is related to the Grid's internal focus state rather than the actual DOM focus.

Environment :

Telerik UI for ASP.NET Core
Kendo UI version: 2026.2.520
Popup editing mode
Grid is not configured with .Navigatable()
Reproduced in Edge Chromium

Actual Behavior:

Open a Grid popup editor.
Close the popup using the Window close button (X).
A Grid cell keeps the k-focus CSS class.
The focus outline remains visible.
Expected Behavior

Where Navigatable is not set (false), losing the popup using the Window close button should clean up the Grid focus state, or behave consistently with other popup closing mechanisms.

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

There appears to be a bug in the Grid component when used with a ContextMenu. To reproduce:

1. Create a new Telerik ASP.NET Core MVC application using version 2026.2.520 and select the “Grid and Menu” template.
2. In Index.cshtml, add .ContextMenu() to the Grid, then build and run.
3. Right-click a row → the context menu appears (expected).
4. Stop debugging,
5. remove .Scrollable() from Index.cshtml, and run again.
6. Right-click a row → the context menu does not appear (unexpected).

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

Bug report

When a user creates a filter with a date, it starts as an empty Datepicker, but the value is appearing as an empty string. Thus, if the user clicks apply, an error appears in the console. If you place a value in the DatePicker and clear it, the value will be Null.

Reproduction of the problem

1. Go to this Progress Telerik ASP.NET Core REPL.
2. Add filter for a Date but keep the datepicker empty.
3. Select apply.
4. Now, add a date and clear the value.

Current behavior

The filter menu sends isnull filter queries in the following format:

While the Filter component sends it as follows:

As a result the ToDataSourceResult method fails.

Expected/desired behavior

If the DatePicker is empty, the filter should properly perform the 'isnull' query upon clicking apply.

Environment

• Kendo UI version: 2023.2.606
• jQuery version: All Supported Versions
• Browser: all

### Bug report

When setting autoWidth: true and expanding a node, the popup's width is not adjusted based on the displayed child nodes.

### Reproduction of the problem

1) Enable the autoWidth option and open the DropDownTree.

2) Expand an item. A horizontal scrollbar appears and the width of the popup is not adjusted as expected:

A Dojo sample for reproduction: https://dojo.telerik.com/faeuFFwb/2

### Expected/desired behavior

The width of the popup must be automatically adjusted when expanding an option and the "autoWidth" option is enabled.

### Environment

* **Kendo UI version: 2025.2.702
* **jQuery version: 3.7.1
* **Browser: [all]

Bug report

When a custom bundle is created the kendo.aspnetmvc script is not placed on the correct order. Thus, in some scenarios errors occur. For example if a custom kendo script is created using the following kendo-config.json and MultiColumnComboBox is used with ServerFiltering enabled and error will be thrown:

{
  "version": "2026.2.520",
  "components": [
    {
      "file": "kendo.aspnetmvc.js",
      "features": []
    },       
    {
      "file": "kendo.dropdownlist.js",
      "features": []
    },
    {
      "file": "kendo.multicolumncombobox.js",
      "features": []
    }
  ]
}

Reproduction of the problem

1. Run the attached sample. In the sample a custom bundle as explained above is used. TelerikAspNetCoreApp1.zip
2. Try to select values in the DropDownList or MultiColumnCombobox

Current behavior

The bundle builder allows kendo.aspnetmvc.js to run before the widgets whose UI for ASP.NET Core helpers it augments. The data in the components is not filtered and the following error is thrown:

Uncaught TypeError: kendo.ui.MultiColumnComboBox.requestData is not a function

Expected/desired behavior

The kendo.aspnetmvc.js schould be ordered correctly by the custom script builder, so errors to be avoided and the components to work as expected.

TicketID:

1716198

Environment

• Kendo/Telerik version: 2026.2.520
• Browser: [all ]

Bug report

Reproduction of the problem

1. Open the Demos - https://demos.telerik.com/aspnet-core/pdfviewer/dpl-processing
2. Load the file Test_pdf_png.pdf

Current behavior

An error: Unable to load image 'data:image/png;base64 is thrown in the console

Expected/desired behavior

Loaind images when using DPL is a limitation, but there should be no errors in the browser console even when a file containing image is loaded in the PDFViewer.

Environment

• Kendo/Telerik version: 2026.2.520
• Browser: [all ]

Bug Report

When applying the kendo.aspnetmvc.ready.min approach in the following Knowledge Base articles for PDFjs workarounds(MVC/Core), the watermark and banner display.

Reproducible

1. See attached project: PDFViewerKendoReady.zip
2. Run the project.

Current Behavior

The watermark and banner appear.

Expected Behavior

The watermark and banner should not appear.

Environment

Kendo UI version: 2026.2.520
jQuery version: 4.0.0
Browser: all

Bug Report

When applying the partial view approach in the following Knowledge Base articles(MVC/Core), the watermark and banner display.

Reproducible

1. See attached project: PDFViewerPartialView.zip
2. Run Project

Current Behavior

The watermark and banner appear

Expected Behavior

The watermark and banner should not appear.

Environment

Kendo UI version: 2026.2.520
jQuery version: 4.0.0
Browser: all

### Bug report

On mobile devices, when the TaskBoard columns are filled with cards, the users have trouble scrolling horizontally through the columns. When they attempt to scroll the screen, they accidentally drag cards instead of scrolling the columns. This makes navigation in the TaskBoard quite difficult, particularly for projects with a large number of cards.

### Reproduction of the problem

1. Create a TaskBoard with at least two columns.

2. Fill the columns with cards.

3. Open the browser DevTools and switch to mobile view. Tap a card to scroll the columns horizontally or tap at the bottom of the TaskBoard to activate the horizontal scrollbar.

4. The last card is accidentally dragged.

A Dojo sample for reproduction: https://dojo.telerik.com/izASODan

### Expected/desired behavior

When the user makes a hold/long press/long tap, show the "indicator for drag and drop" and then he/she continues with the gesture by moving the card to the desired column and lift the finger. This way, the accidental dragging will be prevented. For more information, refer to the GitHub issue.

Note: The cards in the TileLayout can be dragged only through the card's title element. The TaskBoard cards can be dragged through the card's body, as well.

### Environment

* **Kendo UI version: 2024.3.806
* **jQuery version: 3.7.0
* **Browser: [all]

As a result of an EF Core issue, the ToDataSourceResult() is not able to perform the query when the DataSourceRequest object contains grouping.

The problem occurs using the query below, assembled by Telerik routine:

var temp = _db.Pessoa
    .OrderBy(item => item.Email)
    .Skip(0)
    .Take(40)
    .GroupBy(item => item.Email)
    .OrderBy(g => g.Key)
    .Select(g => new AggregateFunctionsGroup
    {
        Key = g.Key,
        ItemCount = g.Count(),
        HasSubgroups = false,
        Member = "Email",
        AggregateFunctionsProjection = new
        {
            Count_Referencia = _db.Pessoa
                    .Select(t => new
                    {
                        t.IdPessoa,
                        t.Referencia,
                        t.Nome_RazaoSocial,
                        t.Apelido_Fantasia,
                        t.CPF_CNPJ,
                        t.RG_IE,
                        t.Email
                    })
                    .OrderBy(item => item.Email)
                    .Where(item => item.Email == g.Key)
                    .Count()
        },
        Items = g
    })
    .ToList();

In the routine where the AggregateFunctionsGroup is created, the Items property must not only be the query itself, but also the fields specified in the main Select. Or, the call to the Select() method must simply be added:

var temp = _db.Pessoa
    .OrderBy(item => item.Email)
    .Skip(0)
    .Take(40)
    .GroupBy(item => item.Email)
    .OrderBy(g => g.Key)
    .Select(g => new AggregateFunctionsGroup
    {
        Key = g.Key,
        ItemCount = g.Count(),
        HasSubgroups = false,
        Member = "Email",
        AggregateFunctionsProjection = new
        {
            Count_Referencia = _db.Pessoa
                    .Select(t => new
                    {
                        t.IdPessoa,
                        ...
                    })
                    .OrderBy(item => item.Email)
                    .Where(item => item.Email == g.Key)
                    .Count()
        },
        Items = g.Select(t => new
        {
            t.IdPessoa,
            ...
        })
    })
    .ToList();

This way, the issue does not occur.

Currently, the text in the Grid commands can be customized in Kendo UI for jQuery using the following commands:

• https://www.telerik.com/kendo-jquery-ui/documentation/api/javascript/ui/grid/configuration/messages.commands

However, such options are missing in the wrappers. Thus, to customize the texts of the commands in the edit dialog, the elements must be modifed as in the example below:

 function onEdit(e){
      e.container.closest('.k-window').find('.k-window-title').text('My custom text')
      e.container.closest('.k-window').find('.k-button[ref-update-button]').text('Button Update Changed');
      e.container.closest('.k-window').find('.k-button[ref-cancel-button]').text('Button Cancel Changed');
 }

In addition, it will be good to have an option that will allow customizing the Edit Dialog text