I think it’s probably a bad UX for hitting the 
button in the top-right of the post editor to hide all the fields like title, category, etc.
You go from this:
To this:
Because when you try to click the Create Topic button when you’re done editing, your post won’t work if you haven’t finished filling out those fields. You’ll just get this error:
It tells you to fill the required, but you can’t see them. At least if you forget to fill out Title, it switches you back to the mini-editor so you can see it. But really, I think it should probably just keep these. Maybe have a toggle on the maximized editor to hide them if you really want full monitor composition.