I have a chance to pick up the old Slik U212, which appears to actually be in great shape. My old Slik, can't even tell you which model it is, has seen better days. I like that the U212 can go really low profile for some ground shots. But, I do have a problem. My old Slik, when you secure the Leg Clamps, you can press down on the pan head and the legs stay locked in position, rock steady. No leg shortening. With this U212, I can lock down the leg clamps and with minimal pressure, the legs will shorten up and collapse. Is there something I am missing from my old Slik to this one? Why will the legs not stay secure when locked?