Switching background image to white yields striped screen

[TomCunningham]

I am fiddling around with Chris Spooner's ForecastTime app, adding the ability to invert the clock face.  Here is some of the code:

index~300x300.gui:

   <svg>
   <image id="bgImage" x="0" y="0" width="100%" height="100%" href="blackBackground.jpg" load="sync" />
   </svg>

app/index.js:

   bgImage.href = invert ? "whiteBackground.jpg" : "blackBackground.jpg";

When invert is false the black background shows up just fine, but when invert is true I get this:

The .JPG files are non-progressive 300x300 grayscale 8-bit gamma integer images.  I tried using .PNG files, but the white background in that case doesn't work, e.g. the background remains black.  This only happens on the real hardware (Versa), on the simulator the white background appears as expected.  Any ideas as to what could be going on?  Thanks!