It does seem to work on the test page you provided...
Usually, the whole image needs to be fully loaded when you start plaing with its propreties. Its a possibility that the image was not fully loaded when you start cloning the node. I can't be sure though. Try to add a function to the onload event on your image (not sure if it exists) that will alert a message. See if it pops before or after the width and height assignments.
as fake suggested, use image onload event. , I have created something similar, premii-using-nikon-d70/84" target="_blank" rel="nofollow">http://foto.premii.compremii-using-nikon-d70/84 (try on FF).
After the page is loaded, I am downloading next and previous image, Once next & prev images are loaded, onLoad events get fire.
If you mouse over foto, you will see next and previous arrow buttons after onload events are fired.