为什么 nginx 在使用正则表达式重定向时返回八位字节流？

我正在尝试为 Codeigniter 设置重定向，以便 URL 像localhost/codeigniter/class, 所以 localhost/codeigniter/class. Drupal 8 中也使用了这种类型的 URL，所以我决定使用 regexp 进行重定向：

location ~ /(drupal|codeigniter)/ {
        try_files $uri $uri/ @rewrite8;
    }

location @rewrite8 {
        rewrite ^/(drupal|codeigniter) /$1/index.php;
    }

但是，当我转到该页面时，系统会提示我下载文件（在响应标头中，MIME 类型看起来像octet-stream）。

如果您不使用正则表达式：

location /codeigniter/ {
        try_files $uri $uri/ @rewrite8;
    }

然后一切正常并给出text/html。

什么可能导致这种情况以及如何进行正确的重定向？

UPD。完整配置：

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html;

    # Add index.php to the list if you are using PHP
    index index.html index.htm index.nginx-debian.html index.php;

    server_name _;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
    }

    location /codeigniter/ {
        try_files $uri $uri/ @rewrite8;
    }

    location /drupal7/ {
        try_files $uri $uri/ @rewrite7;
    }

    location @rewrite7 {
        rewrite  ^/drupal7/(.*)$ /drupal7/index.php?q=$1;
    }
    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000

    location ~ \.php(/|$) {
        fastcgi_split_path_info ^(.+?\.php)(|/.*)$;
        include /etc/nginx/fastcgi_params;
        fastcgi_pass unix:/var/run/php-fastcgi/php-fastcgi.socket;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME /var/www/html$fastcgi_script_name;
    }

    location @rewrite8 {
        rewrite ^/(drupal|codeigniter) /$1/index.php;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #   deny all;
    #}
}