PCD8544 display behaves differently with saved()'ed code

I have some simple temperature display code which is giving me grief when I save() it to the Espruino. The code continues to run after a reset or power cycle but the characters are barely visible on the screen. It's like the contrast is turned down to almost zero. It works and displays fine when the same code is just uploaded and run directly. I've read all the threads about using onInit() but it's not helping at all.

Any ideas? Code looks identical in both cases using dump() apart from the contents of g.buffer;

Thanks

var g;
var rtc;
var numReadings = 10;
var temperatures = [];
var index;                  // the index of the current reading
var total;                  // the running total
var average;                // the average

function onInit() {
  index = 0;                  // the index of the current reading
  total = 0;                  // the running total
  average = 0; 
  SPI1.setup({ baud: 1000000, sck:B3, mosi:B5 });
  clearInterval();

  // initialize all the readings to 0:
  for (i = 0; i < numReadings; i++){
    temperatures[i] = 0;
  }

  digitalWrite(B13,0);
  I2C2.setup({scl:B10,sda:B11});
  rtc = require("DS3231").connect(I2C2);
//  setInterval(function() {
//    console.log(rtc.readDateTime());
//  }, 1000);

  g = require("PCD8544").connect(SPI1,B6,B7,B8, function() {
    g.clear();
    g.setContrast(0.45);
    g.flip(); // copy this to the screen
    setInterval(onTimer, 1000);
  });
}

function onTimer() {

  // subtract the last reading:
  total = total - temperatures[index];

  var val = analogRead(C0);
  temperatures[index] = (((val*3.3)-1.25)/0.005);

  //console.log("Total: " + total);
  //console.log("Temperature: " + temperatures[index]);

  // add the reading to the total:
  total = total + temperatures[index];

  // advance to the next position in the array:
  index = index + 1;

  // if we're at the end of the array...
  if (index >= numReadings){
    // ...wrap around to the beginning:
    index = 0;
  }

  // calculate the average:
  average = total / numReadings;

  //console.log("Average: " + average);

  g.clear();
  g.setContrast(0.45);
  g.setFontBitmap(); // simple 8x8 font
  g.setFontVector(20); // large font
  g.drawString(average.toFixed(2), 0, 0);
  g.drawString("C", 65, 0);
  g.setFontVector(15); // large font
  var localtime = rtc.readDateTime().split(" ")[1];
  g.drawString(localtime, 0, 32);
  g.flip(); // copy this to the screen
}

onInit();