GFCI Test not working... only while in the box
I have a GFCI outlet on a kitchen wall. It has power and the Reset button is pressed in. The problem is when you press the Test button, it doesn't shut off the outlet. I tried pulling the GFCI out of the box and while it is pulled out of the box, the Test button works fine. However, as soon as I put it back in... it doesn't work.
The box that it's going in is metal with a ground screw that is connected to the GFCI ground. The only other thing that seems unique is there are two nails driven through the inside of the box, presumably to anchor the box to the stud. I've just never seen one mounted with the nails going through the middle of the box. Is it possible that these nails are causing the GFCI to not work?