You're not supposed to rotate the knees manually. That's how IK rigs are supposed to work. The pelvis and feet are the parts you're supposed to move. The position of the knees is calculated automatically. The knees' "rotating sphere" as you call it, is only meant to control the direction the knee will point towards. Rotating that sphere will not rotate the knee, but when you move that sphere left or right, you see the knee will move to be pointed at it. The same applies to elbows.
tl;dr: u r dumb