bluetooth failing when not connected to USB

Hi

I have a little test script running fone when connected to USB:

var s = require("servo").connect(B13);

var curBuff = "";

Serial1.on('data', function (data) {
  try{
  if (data==","){
    s.move(parseFloat(curBuff));
    curBuff = "";
  }
  else{
    curBuff += data;
  }
  }
  catch(err){
  }
});


// keep track of the next LED
var next_LED = 1;
// keep track of the ID, see later
var timeout_ID;
function swap() {
  // remove the timeout to turn of all LEDs when the user pressed the button
  if (timeout_ID !== undefined) {
    clearTimeout(timeout_ID);
  }
  // determine which LED to turn on/off
  switch(next_LED) {
    case 1:
      LED3.write(1);
      LED1.write(0);
      s.move(0.5);
      break;
    case 2:
      LED2.write(1);
      LED3.write(0);
      s.move(0);
      break;
    case 3:
      LED1.write(1);
      LED2.write(0);
      s.move(1);
      break;
  }
  // determine the next LED to turn on
  next_LED = Math.wrap(next_LED, 3) + 1;
  // prepare a timeout to turn off all LEDs after a while
  // we capture the ID here, so that we can use it in a next call to this function
  timeout_ID = setTimeout(function () { LED1.write(0); LED2.write(0); LED3.write(0); timeout_ID = undefined; }, 5000);
}

setWatch(swap, BTN1, {repeat:true, edge:"rising"});

If I send messages to the bluetooth connection from an app on my phone, first a string of a float (e.g. '0.1') then post another BT message containing just a comma ',' the servo moves.

I can disconnect from the WebIDE. It still works.

However! If I unplug the USB, I get a BT message back from the board to my phone:

'Console Moved from USB'
Now it fails to work. I send it the float, it echos it back. I send the comma, its sends error:
"Uncaught SyntaxError: Got ',' expected EOF at line 1 col 1
,
^"

Any help appreciated. :)
Phil