Okay, I tried the "Prime Auto Inc even if not necessary". The buttons show up okay. Rather than explain what's going on with my own app, I loaded up the example app: web3.app, added the copy button both inline and on the form, set the MailboxesFormControl to Prime auto inc... and the same thing happens, Nothing shows in the form. I would expect that the value from the record I'm copying would show up in the new form.
Here's the other oddity: If I press CANCEL, it adds the record with the next SysID, but there is no value in the fields. I've tried installing a few times. Any ideas of what else I can look for?