[Zope] Changing the properties contained in the default PropertySheets

I have created a custom view for the properties of my python product object. I allow the user to change the properties in the custom form. After the user if finished editing the properties, he clicks on the Save Changes button. This calls on a dtml method that calls the manage_changeProperties(REQUEST) function. However, the changes are never made to the actual properties of the object. I have tried several different ways and still fail. I would greatly appreciate any guidance provided. Stacy