Multiple TinyMCEs breaking Distraction Free Writing

Don’t use meta boxes for TinyMCE. It has some kind of conflict with the DOM. Hook your code including wp_editor to edit_page_form action instead:

add_action( 'edit_page_form', 'my_second_editor' );
function my_second_editor() {
    // get and set $content somehow...
    wp_editor( $content, 'mysecondeditor' );
}

See Notes on wp_editor in the Codex.