Kirk and Dennis,
We have been complaining about this for many years--back when Rob Galbraith's forums were still active in fact. The answer was the same then.
Overall, your support is the best in the business, but in this specific case, I think you have dropped the ball. Blaming Apple for the problem doesn't get us a working Undo. Is Apple actually negligent in fixing a bug for six years running or do they insist that Undo should not be used in a modal dialog and this will never change?
It is far past time to fix this problem. If that means making the IPTC dialog non-modal, then please make it non-modal.