The demo I posted link to(http://demos.telerik.com/silverlight/#PropertyGrid/ManuallySetDefinitions
) is in fact not using auto generated fields. Do you get the same behavior on it ?
Furthermore, in case this example does not help, it would be great if you could send us a sample project illustrating your settings and requirements. Otherwise, all my suggestion would be only guesses based on probably more common scenarios.
the Telerik team