Have had similar experiences to what's been reported here so far, more or less since Bionicle's day-one. Though very recently, I've seen it most in the translucent Inika sockets, both single-socket/hand pieces and double-socket/arm and leg pieces. I bought a few at BrickLink the other day, and since they arrived, every single one of them has broken at the socket, just from connecting the ball. Righteous pain in the backside, one and all.