Precor treadmill's calorie counter changed

Three times a week I go to my local Y, get on a Precor treadmill, and walk uphill for an hour. These are the fancy networked machines with internet and TV, and you have a personal account that logs your progress.

At my age, weight, incline, and speed, the Precor treadmill reports I always burn ~600 calories during my workout.

Today I did the same workout, but it reported I only burned 515. I checked my age and weight settings. They are still correct.

So which has happened:

  1. Faulty machine
  2. Precor updated the software with a new algorithm for all of the Y’s machines
  3. Precor is punishing me for always doing the same workout

?