For whatever it's worth, and it may work differently for others (I'm normally on a PC, using FireFox), I simply reload the page when that happens to me; my reply reloads too and then I can just submit it. I usually copy my reply text just in case it doesn't reload when I reload the page, but I can't remember when it hasn't; still, better safe than sorry. Don't use the back button or click on the "Knives Forum" link and go back into the thread -- just reload the thread page and then you should be able to submit.