Closing the vent will stabilize the heat, and the element won't have to come on as often.
You know, there's this other test I ran, and I don't understand it either. I put five thick steaks on the top two shelves. Before I put the steaks on, temperatures matched (vent may have been closed to help it heat up faster). After I put the steaks on, I could repeat these results multiple times:
1) open the vent -> temperatures diverge by maybe 20 degrees (MES reading higher)
2) close the vent and let temps stabilize -> temps match within a degree!
That does imply that something else is going on that I don't understand.
However when smoking, closing the vent will hold smoke in keeping it from leaving & making it stale. Not a good idea.
Given time they will both stabilize, maybe at different temps, but stabilize.
It takes the Maverick or the ChefAlarm longer to stabilize because they are not connected to a wall, and are therefore moire sensitive.
However like I said before, you can't fault your smoker for it's readings with meat in it---That would be the things you are doing (placement of the sensors, temp adjustments, etc).
Testing while empty will tell you about the Smoker itself.
I hope that helps,
Bear