Tested on both Firefox 2.0.x and Firefox 3b4.
I don't understand the bug. If I enter some text into both elements, and submit the form, then go back to it, form fill works fine for both of them, even if I reload. Can you provide more detailed steps to reproduce?
Fill the form, than hit the reload key. The left field stays filled, while the other not. The history seems to work well, since I can do the path of fill, submit, backward successfully, but even than the field losts its text after reloading the page. Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9b4) Gecko/2008030318 Firefox/3.0b4
Oh, that has nothing to do with the form autocomplete. The form state restoring code handles those cases, and since the element isn't in the document when the page is initially loaded, I suspect this is INVALID.
This might be a duplicate of bug 285730.