The sh.setBalancerState() function in the mongo shell is coded thus:

sh.setBalancerState = function(isOn) {
    if (isOn) {
        return sh.startBalancer();
    } else {
        return sh.stopBalancer();
    }
};

As a consequence, running sh.setBalancerState("true") actually stops the balancer, as does sh.setBalancerState(). These are surprising results.

Suggest adding a type check to the code before the if statement:

  if ((typeof isOn) != "boolean") { print error message and exit }