<telerik:RadNumericTextBox ID="RadNumericTextBox1" runat="server" MinValue="-999" MaxValue="999" NumberFormat-DecimalSeparator="," Type="Number" AllowOutOfRangeAutoCorrect="false" DataType="System.Decimal" NumberFormat-DecimalDigits="4"></telerik:RadNumericTextBox> 1) type in "12345,4321" 2) blur and the control give an error. The typed value became: "12345.4321" 3) The comma "," decimal separator is changed into dot "."