I'm not sure if mine's defective, but it's my first diy. It seems that it's not very stable, so I tightened the screws and have been moving the sides around to try to break it in. However, it still seems that it pops sometimes, and that on a couple of sides, when you move it, you can literally orientate the corner piece that's going to the bottom, and there's a problem with the pieces getting caught on the center piece while doing this, so that it's wobbly. I haven't lubed it yet or untightened the screws, which is not such a good idea, since it keeps popping. Overall, the pieces just seem, er.., sproingy. On one side, the screw won't really go all the way in. I'm not sure if I should switch it with another side. Any admonitions are welcome.
(On a side note, I can't seem to upload an avatar, even though my image meets the limits.)