I think I've run into a bug similar to:

http://dev.jquery.com/ticket/3988

In particular, when a page that is inside a frameset uses $(document).ready, it will not be fired until after the images load, while the same page run on its own fires the event immediately.

To reproduce this dynamic images that are noticeably slow to load are required, but I haven't been able to find any that are publicly available to include in my example. If you load the inner page (test.html) in IE6, you will see that the event it raised before both images is loaded. In the frames version (test_frame.html), though, the event will not be fired until after the images load.