SPUtility.ValidateFormDigest breaks ASP.Net server side validation

I have a Web Part which is using SPSecurity.RunWithElevatedPrivileges, and thus needs to call SPUtility.ValidateFormDigest. However, this apparently causes it to ignore all ASP.Net validators server side. The validation functions are being called, but the IsValid result seems to be either overwritten or ignored. What is causing this, and how do I fix it?