The RME error page said that I was not logged in, implying that I need to re-authenticate -- and yet the page did not contain any kind of login link. If there had been a login link then I would have clicked it, and furthermore I would expect my text to be preserved throughout the login process, so that after logging in I can re-submit my text (lots of web sites do this).
I don't recall the error page asking me to click Refresh -- and anyway, this makes no sense! Either a session is valid, or it's invalid and you need to re-authenticate.
Yes I am aware that the text is stored in the browser, but the default behaviour in modern browsers (unless overridden by the web site) is that when you click Back/Forward, pages are retrieved from the browser's cache and the contents of forms are preserved. I use Chrome and 98% of web sites behave like this.
When you click Back and your form data has vanished, it is because the web site is doing something to actively break this functionality. For example, setting unnecessary no-cache headers. I don't think you should break this standard browser behaviour unless you have a specific reason to.
Since there was no Login link, clicking Back was the only option I had. Please don't tell me I was "wrong" to click back: if the web site was properly behaved, my text would still have been there, and then I could have copied, re-authenticated, and re-pasted the text.
So I still maintain that with the weird session timeout behaviour, the unhelpful error page, and breaking the back-forward cache behaviour -- the web site is at fault in this case.