Hello SivaPrasad Bevara,
This is an expected behavior. When you hit the control it gets the focus first and then passes it to the TextBox in it. That is the reason the lost focus appearing. You may need to perform a check if you are still in the control. Unlike WPF in Silverlight there is no such property that can tell you if the focus is somewhere in your control. (WPF - UIElement.IsKeyboardFocusWithin).
All the best,
the Telerik team
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