What happens when you clear your browser's cache and try the script again? From the jQuery load() docs:
It is possible that the load event
will not be triggered if the image is
loaded from the browser cache. To
account for this possibility, we can
use a special load event that fires
immediately if the image is ready.
event.special.load is currently
available as a plugin
In general, it is not necessary to
wait for all images to be fully
loaded. If code can be executed
earlier, it is usually best to place
it in a handler sent to the .ready()
method.
So it sounds like your cached image isn't triggering the load event, so you may want to try the plug-in that's mentioned. You can find the JS file to download here.
Hope this helps!