Created a question. Then found out I'm not logged in. Tried logging in using the link at the bottom. Clicked on MyOpenID. Was redirected to MyOpenID. Got it wrong. Got back. Click on "other options". Selected my correct OpenID info. was logged in, but it redirected me to the home page. Didn't want to lose my question, so I went back three times to get to the Ask Question page. My question was retained BUT it indicated I was not logged in. Than I thing I tried to log in again - error.
This is expected behavior and not a bug.
Pressing the back button a few times after logging in gets your browser in an incorrect state, in which you just load the page where you were logged out. But actually, you are logged in. So, if you try to login again you get an error because you are already logged in, that makes sense and is not a bug.
What you should have done instead is just click on
The same happens for answers, after typing this out and waiting some seconds I refreshed this tab after which my answer was still here. So, there is not really something to worry about. If you are uncertain whether it is kept, you could copy paste what you have written (or go back with the back button, then copy it, then go forward again) or use an extension that remembers what you write in text boxes for a set amount of time.
You could see the back button as something that takes you back in time to where you were earlier, which might not visually represent "now" but note that actions are applied to "now" and not to back then...