RadButton's clicking is triggered when the following conditions are met:

-input type="text" handles onkeypress event

-onkeypress event focuses the RadButton

-the key pressed that is handled by onkeypress event is Space or Enter

Triggering the clicking with "Space" can be workaround by setting some timeout to the focus(). For example:

ASPX:

        <telerik:RadButton ID="RadButton1" runat="server" Text="RadButton"></telerik:RadButton>
        <input type="text" name="name" value=" " onkeypress="KeyPressed();" />

JavaScript:

        function KeyPressed() {
            setTimeout(function () {
                $find("RadButton1").focus();
            }, 200);
        }