We have had problems with RadMaskedTextBox showing the EmptyMessage since upgrading to 2012 Q2. Previously this was not a probhlem. The following markup just shows the expected input rather than the empty message.
See the attached screenshot.
<telerik:RadMaskedTextBox ID="SSNTextBox" runat="server" EmptyMessage="SSN" Mask="###-##-####" />See the attached screenshot.