I had this problem tonight...when I slid the door off to switch out the battery, I noticed that the magnet had come off the door and was stuck on the other magnet on the unit.
Well, I put the magnet back in it's place and pushed it in... but I placed the battery incorrectly (wrong polarity) and now the door would not fall into place over the magnet on the unit
Now, why in the world would the magnet come off. Well, I have a habit of clicking the door up and down as I hold it, and I hold my mini dearly practically all day long!
I guess all of the friction loosened it over the past two weeks. Now, anything out of the ordinary happens to my mini and right away I email our fearless vaper, Robert.
Anyways, I got a small piece of duct tape and rubbed it over the spot with the magnet...after several times, viola! The magnet came up on the tape, and I was able to place the magnet back on the door correctly.
Of course in the meantime, dear Rob emailed me back some suggestions - one being that when replacing the battery, use a dab of super glue. I heart Rob
All is well in Reoville.