Last week, I called to make my ADR's and the only time available for Chef Mickey's on the date I wanted was 7:50. Since we were supposed to go on the fireworks cruise that night, I booked Chef Mickey's for a different night instead and booked 'Ohana that night.
Less than 30 minutes later, I was regretting my decision - Chef Mickey's on our arrival day has become tradition, and the fireworks cruise was an expensive whim. So I called back, booked Chef Mickey's for the first date at 7:50 and switched 'Ohana to a later date. Then I asked the CM to cancel my first set of ressies.
He told me that in the new system, I should have just given him my original reservation numbers, and he could have modified them, so that I'd have the same confirmation numbers, and the system would automatically remove the old ADR when we added the new. I apologized, and he said I had no way of knowing, but he was telling me for next time.

Guess he could tell I was a waffler, huh?
But anyway, the new system should make cancelling ADRs more frequent, since modifying your reservation automatically cancels your old one.