To make a long story short, I found that the previous homeowner had used a plastic butter dish to stop a water leak from the shower valve. After removing a shelf in the closet and opening up the wall, I found that the copper pipe to the showerhead had been connected to the shower valve with a short section of plastic hose, hose clamps and a black steel nipple that is only supposed to be used for running gas lines. My repair included installing a ½ inch male brass compression adapter and a short section of copper pipe.
From what the customers told me, the previous homeowner was basically an idiot when it came to home repairs. I would have to agree.