This just happened to me. I placed a couple of boxes in the trunk of the car, closed the trunk, everything OK. I make a stop, open the trunk. When I close it, it stays shut for a few seconds and it pops open. Eventually, I get it shut after repeated attempts. Car was running when I tried to close the trunk. When I got to my destination, had the same problem. When I emptied the trunk and closed it, it worked fine.

Any thoughts?

 

Did you leave you leave your key fob in the trunk?
If you did that's why it won't close

 

Exactly as above, maybe your keys were in one of those boxes. When you leave the keys in the trunk accidentally it wont close, rather cool feature! Try it out sometime.