[Zope] ZCatalog - Full Update Deletes Valid Entries

I have a CatalogAware ZClass. It puts itself into the the catalog quite nicely, and shows up in the Catalog tab properly. I create a new instance of this ZClass. All is well. It appears in the catalog. If I go to its entry in the catalog, select it, hit update, no problem. Still there. If I go to Advanced, and hit Update (full Catalog update), the entry disappears. If I got to Find Items, select my ZClass, and add them back in, they come back. A full update now no longer causes them to disappear. Just like my last problem, this did not always happen. To my knowlege, nothing has been changed. Of course, my knowledge is lacking, which is why I'm writing this message. Thanks in Advance. Edward