Bug report

When the TabStrip has an empty dataSource initially, and then a new item is added using the dataSource.add() an error appears in the console and no item is added.

Reproduction of the problem

1. Run the example and observe the console - https://dojo.telerik.com/nzQDTrjN

Current behavior

An error appears in the console, and no item is added.

Expected/desired behavior

An item should be correctly added in the TabStrip.

The issue is a regression starting with the KEndo version 2025.3.825

Workaround

Add an item in the dataSource initially and remove it when needed - Dojo - https://dojo.telerik.com/NgHHVOFy

Environment

• Kendo UI version: 2025.4.1111
• Browser: [all ]