MaskedEdit not clearing

I have a TextBox on a ListView InsertItemTemplate with a Mask and validator for a date that is giving an error about an invalid date and not sure why.  Below is my TextBox, validator and mask controls.  The date is bound to a date column in SQL table and want to send null if no date is entered.  Any help is appreciated.

<asp:TextBox ID="txtLicenseExpires" runat="server" Text='<%# Bind("LicenseExpires","{0:d}") %>' Width="80" /><asp:CompareValidator ID="dateValidator2" runat="server" Type="Date" Operator="DataTypeCheck"
                            ControlToValidate="txtLicenseExpires" ErrorMessage="Please enter a valid date." Display="Dynamic"></asp:CompareValidator><asp:MaskedEditExtender ID="MaskedEditExtender1" runat="server" 
                            TargetControlID="txtLicenseExpires" MaskType="Date" Mask="99/99/9999" 
                            ClearTextOnInvalid="True" ClearMaskOnLostFocus="True"></asp:MaskedEditExtender>