One more thing you might want to consider:

I've only had the read-only message happen to me once, so I can't test this for that, but right after I posted my last reply (successfully), I hit the Brower's page back button (left arrow, ALT/left arrow on the keyboard, whatever) to go back to the previous page.  The complete reply text was still sitting in the rich text edit box, waiting to be copied, perchance to be re-pasted somewhere else.

I hope this suggestion is useful.