Thank you for the screencasts. I believe that this behavior is expected and I cannot confirm it as a bug. The "required" attribute of the select element, means that the validation will pass if there is any value. As you probably know, the combobox widget allows custom value. Hence when you type "Item" the value of the combobox is "Item" and the validation passes. You can prevent custom value wiring the change event and clearing the combobox's value using value method. Check this link for more information.
All the best,
the Telerik team
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