Someone mentioned earlier there may be a "system glitch". That may be true, but in my mind I would be willing to bet the bigger issue is the amount of folks who are double/multiple booking ADRs. Not sure if you want to eat at 'Ohana or Kona....folks are simply booking both.
Book a reservation, and then try to book another reservation for the same date and time. When booking the second reservation the system will provide a notice stating you have a duplicate ADR for the same time and ask if you want to cancel the first reservation or keep both. There is no incentive not to double book as the current system doesn't prevent it from happening. IMHO, that is why it is difficult to secure ADRs for places like 'Ohana even though people try to make reservation 180 days prior to their trip.