I sliced a large image 1600px wide into two pieces. When I browse the page and press menu buttons there is a blindingly noticeable flicker in which the background shows through precisely the size of the slice.
Are there any possible causes to why this might happen?
You are hitting the web server so you will see different results everytime. You are basically reloading the page. Have you tried viewing it with a 56k modem? You might find that you will have a longer flash the slower the connection. The browser gets the code then loads the images from cache. Your images are larger so it takes longer to grab and display.