What do you mean by Shorted?
Auto fired when screwed in?
The only thing that will cause that is forcing the negative contact Pin higher than the Delrin.<Unless your Battery has a tear in the wrapping touching the mod itself.>
Oh, and that rice pin people keep taking out to reduce bind.............It also helps to transfer current from the center(contact pin) to the Brass threaded section and Body of the mod. I.E. part of the current path.
I assumed it was shorting but maybe I used the wrong word the button heats up, and occasion there seems to be a voltage drop (have not measured) as vapor production is reduced