Now, perhaps there is no need for new software for the forum, perhaps a small patch could resolve the issue.
Won't that need to involve the server in one way or the other though? Unless you're talking about client-side caching with some plugins or something similar. I'm not familiar with how it works, it would be neat if that is possible as long as it doesn't bog down the browser due to too much caching.
So far I did what loyce said, and tried to click preview as often as possible if I need to type a very long post.
Also in my Android too the situation is same but where we most likely will refresh the page while swiping down and all the text written will be gone but its unlikely to happen with PC.
Don't most browsers open the typing window when you click the posting page? Maybe you can change the gesture of your browser or Android so you don't mix refresh and scroll down.