Temp off on the Maverick?

First post, I've been lurking stealing ideas for my table, recipes and advice. To all who have contributed unknowingly, thank you...I'm having a blast with my LBGE. I just got the Maverick 732 for my birthday. Did some chicken thighs, raised grill. (stolen recipe from forum). Had the temp steady at 400, the temp probe was on the bottom rack and it was reading very close to dome temp for about 30 min of the cook. I did calibrate the dome thermometer when I first got my egg (stolen idea from forum). Then after the steady 30 min cook, the temp on my Mav shot to 450 degrees. I figured flare up and went to check. All was good, the dome read 375 and steady, the Mav climbed to 500. I tried resyncing and/or power on - off. Temp stayed steady at 500. Then as I'm writing this, I went out to pull the corn in husk off the grill...the Mav and the dome were exact. So confused. Is this a normal or did I get a lemon flavored Maverick? Thanks for any input.