I tried that. I've almost got it right. Everything's Null except the "date deleted" field, which is stuck on "0". I tried removing all content from fields, hit save, that did the trick - the columns were blank, but there was no Null. I edit again, this time selecting the Null checkboxes, but strange things happen. I remove the 0 from the "date deleted" field, try to set it to Null, but then the other Null fields revert back again to that "hash" code, with the Null checkbox de-selected.

Even if I remove all content and then try to set them to Null, it won't let me. I can do a few, but can't get them all to change and stay changed at the same time.

Jason