The haki turns a human's limbs into metal limbs, right? And after you disable it, it turns back into human limbs again, right? Well, if you give haki to an android, the limbs will turn back to rubber! I am assuming that this happens because it checks if the limb was human, then if it actually isn't, it thinks that it is Luffy or someone who ate the gum-gum fruit, not an android. Also, I think you could use the same code from the haki to turn devil fruit eater's limbs into metal when they touch water so that they actually sink and don't just get electrocuted. I'm not sure about that.