Mine is doing the same thing. Have you figured out the reason yet?
John, does your unit register the temperature accurately? The only thing I can think is if the PB internal probe is off, as if it is saying need more heat, not at set temperature.
I use a secondary probe on the shelf at food level, which is higher than the built-in probe and temperatures in that area run 15-20° higher on mine.
Make sure your auger is not running constantly.
I have seen my 3 series vertical overshoot like that, but it is on the first heat-up, once the pan is filled with water, it will settle down after a bit. I think it is normal as long as it doesn't go too much more than 40 or so degrees over.
Try it again and see how it acts. See if it settles down when it's heated up. Make sure the built in probe is clean as well.
Don't leave it unattended, either, just in case it does not stabilize.
Good luck, keep us posted.