Which is that for some people there’s a UI bug that puts the “Exit Mobile Version” banner over the “Post” button when you want to leave a comment. I verified it being an issue on Android; I haven’t checked it elsewhere. I’m looking into it to see if I can fix it.
In the meantime, if you experience this bug in mobile, the simplest workaround is to exit the mobile version, and then leave a comment using the non-mobile theme. The non-mobile theme should still format to look legible on phones and tablets, and the comment functionality is not obscured by poor placement.