This is really strange. I copied code from RF tutorial (http://livedemo.exadel.com/richfaces-demo/richfaces/fileUpload.jsf) and it still works this way.
After "Add..." i click "Update" and entire page is being submited. Right panel with images is not updated with ajax. Probably it's more general problem. Maybe caused by improper Ajax events posting?
I tested it also without modal panel. It did not change anything.
Can you please minify example and post full page(s) code?