[CentOS] haproxy + Apache + virtual hosts -> wrong host is displayed

Hello,

I hope my question is not off-topic here.

On CentOS 7.2.1511 I have installed:
haproxy-1.5.14-3.el7.x86_64
httpd-2.4.6-40.el7.centos.1.x86_64

The /etc/haproxy/haproxy.cfg binds HAProxy to
ports 80 and 443 and accepts HTTPS to slova.de:

defaults
    mode                    http
    option http-server-close
    option forwardfor       except 127.0.0.0/8
    option                  redispatch
....
frontend public
    bind 144.76.184.151:80
    bind 144.76.184.151:443 ssl crt /etc/pki/tls/certs/slova.de.pem
    reqidel ^X-Forwarded-Proto:
    reqidel ^X-Forwarded-For:
    reqadd X-Forwarded-Proto:\ https if { ssl_fc }
    option forwardfor
    default_backend apache

backend apache
    server domain 127.0.0.1:8080

The /etc/httpd/conf/httpd.conf binds Apache
to port 8080 and serves several Wordpress sites:

Listen 127.0.0.1:8080
ServerName 144.76.184.151

<VirtualHost 127.0.0.1:8080>
    DocumentRoot /var/www/html/afarber.de
    ServerName afarber.de
    ErrorLog logs/afarber.de/error_log
    CustomLog logs/afarber.de/access_log common
</VirtualHost>

<VirtualHost 127.0.0.1:8080>
    DocumentRoot /var/www/html/ruhrgebietsingle.de
    ServerName ruhrgebietsingle.de
    ErrorLog logs/ruhrgebietsingle.de/error_log
    CustomLog logs/ruhrgebietsingle.de/access_log common
</VirtualHost>

<VirtualHost 127.0.0.1:8080>
    DocumentRoot /var/www/html/bukvy.de
    ServerName bukvy.de
    ErrorLog logs/bukvy.de/error_log
    CustomLog logs/bukvy.de/access_log common
</VirtualHost>

<VirtualHost 127.0.0.1:8080>
    DocumentRoot /var/www/html/slova.de
    ServerName slova.de
    ErrorLog logs/slova.de/error_log
    CustomLog logs/slova.de/access_log common
</VirtualHost>

When I open http://slova.de or https://www.slova.de
they work fine. But when I try to open same URLs
with "www." prepended, the browser displays
http://ruhrgebietsingle.de (the 2nd site out of 4)

Why does it happen? I just can not figure it out.

What tool would help here to debug?

Thank you
Alex