I bought brand new shrub irrigation heads by Orbit, the 180 degree type, and I went to adjust one head, which didn't do anything (turning the screw, one by one the others just popped off, and I lost the white pieces inside, no idea where they went. When I say the heads popped off, I mean the adjustable pieces that screw into the body of the part that screws onto the PVC irrigation pipes. That stays on, the inner pieces are flying off. Not sure why they would do this, but the threads don't look damaged or anything. Any idea how to adjust these things and what would cause them to fly off? The old ones did not do this. Thanks!