The design intention is that it doesn't matter how you move the knee - the joint is supposed to sort itself out and ensure only the upper joint moves in the normal bend region while the lower joint is locked out, then for deeper bend only the lower joint moves while the upper joint is locked out. It's actually very clever, and when they are working properly as mine are i can just bend the knee holding a thigh and calf and the joint does its magic. The problem is that the internals of the lower joint just can't reliably take the torque they are subject to when the lower joint is locked out and the result is the mashed internals we are seeing. I personally wouldn't recommend just clipping the whole tab off. By doing that you are defeating the clever mechanism they have engineered and just giving yourself two independent joints. You could say well that's good enough for any other figure with normal double joints, but I think it's a shame to clip 44 when @Jarrod and @BrutiKing's equally simple fixes will get the joint working properly. Also if your joint is already damaged inside, clipping off the tab might not help. You may be in a situation where the internals are so mashed that the lower joint is gonna prefer to spin instead of ratchet properly no matter what the tab is doing. If you're in that situation only BrutiKing's glueing fix will help you. That's probably the most robust long term fix anyway until someone figures out there really was a good reason those two internal parts are separate, but so far I can't and even though my joints are fine I'm inclined to fuse those parts for long term reliability.