Render Pattern not working in SharePoint 2010

SharePoint 2010 uses an XSLT rendering system for displaying field values in list views. If you have custom field types that use the construct for modifying the display value of a field in SharePoint 2007 you will find this no longer works. But backwards compatability saves the day, just add TRUE into your field type declaration and the XSLT rendering will be ignored and legacy CAML rendering will take its place.

XSLT rendering is still used to render the field value, but the value is first transformed using the CAML render pattern before being passed into the XSLT