I don't see how your shower head knows what type of pipe you used. If this is a tub/shower, there is a problem with the diverter in the tub spout. When the pressure is turned off the diverter (in the tub spout) should fall back in place, thus releasing the water in the riser to drain back out and eleminate any leaking. Check to be sure the diverter is acting right before opening any walls.
We'll be glad to help further with more details frunished by you.