ASPxTokenBox – The validation error isn't hidden after a token is selected

Dear Support team

I try to use aspxtokenbox for required field.So I set it as the same as other controls as you can see in the attached code the tokenbox is set as  the same as combobbox. After run and select the value the the alert text is not cleared but combobox work as well.

Please suggest me how to clear the alert text.

C#
<dx:ASPxTokenBox ID="ASPxToken1" runat="server" AllowMouseWheel="True" Tokens="">  
                        <Items>  
                            <dx:ListEditItem Text="a value" Value="a" />  
                            <dx:ListEditItem Text="b value" Value="b" />  
                        </Items>  
                        <ValidationSettings Display="Dynamic" CausesValidation="True">  
                            <RequiredField IsRequired="True" />  
                        </ValidationSettings>  
                    </dx:ASPxTokenBox>  
                    <dx:ASPxComboBox ID="ASPxComboTest" runat="server">  
                        <Items>  
                            <dx:ListEditItem Text="a value" Value="a" />  
                            <dx:ListEditItem Text="b value" Value="b" />  
                        </Items>  
                        <ValidationSettings Display="Dynamic" CausesValidation="True">  
                            <RequiredField IsRequired="True" />  
                        </ValidationSettings>  
                    </dx:ASPxComboBox>