I don’t know how correctly I understood your text, but on my laptop, when I write a post, press the back button, and then click again on the page to print the post, everything is saved. Maybe the problem lies when using mobile gadgets. I deliberately tried to do this, but maybe this happens after a pause.
It same on my end, after reading your reply I thought it was just maybe because of a browser extension or plugin installed that I didn't encounter what OP did. So I just do it now intentionally, I tried to compose a text message and then simply clicked the back button, and when I clicked the forward button, the message was still there. Maybe it was the reload/ refresh button that OP accidentally clicked?
I tried this as well on my Android device, Chrome browser and I didn't encounter losing the post, it only happens when I reload the page.