Alright, I probably won't try to provide pictures here, since this is a fairly easy issue. Essentially, the way the leg panels fold out is such: Kneecap rotates forward. A projection on the kneecap pushes out the top/larger leg armor panel. The bottom edge of this panel pushes out the top of the bottom/small panel, causing the bi-angle look of the armor. When you fold the foot, and it draws the kneecap back into vehicle mode placement, the pressing tab on the kneecap lets go, and a spring inside the bottom/small panel pulls it back in. The top of the bottom/small panel, of course, pulls the lower end of the larger panel back into place as a result. The problem with non-functional pieces seems to be a bit of sprue on the edge of the small panel. It rubs against the side of the cavity the panels fit into on the leg, and causes the panel to exert too much friction for the spring or tab to overcome. As a result, when the kneecap tab presses, the panels refuse to push out, and/or when the spring pulls them in, they won't go because the spring can't pull hard enough. Solution is fairly simple. Lift the top edge of the bottom/small armor plate away from the larger plate with a thin tool, being careful not to harm the paint on either. Carefully pry the bottom/small plate out of the leg (it's just got little pivot-nubs that secure it, nothing major). Pull the plate away from the leg a little, being VERY careful not to overstretch the spring. If you overstretch it, it will fail to be strong enough to pull the plate in even after fixing it. Check the edges for sprue remains or flash, and carefully trim them flush, being very careful NOT to cut away the two intentional nubs that hold the plate in the leg. Then, reinstall the plate, and the gimmick should work perfectly.