It's supposed to be below on mobile because there's not enough room for the feature buttons and the post button on the same row. Will review adding btn-sm-block so Post and Cancel buttons will expand the full width and be more noticeable.
forge.joomlapolis.com/issues/7230
The below is how it'll look as far as the Post and Cancel buttons are concerned after being changed.
Will probably be making the right side feature buttons bar collapse into the top as well if there's room.