I found the reason, but not the solution.
For my IP: 188.8.131.52 I have 3 sites:
According to Apache, default site is aaa.domain.com
Due to the fact that www.example1.com is first in the configuration file, it has the highest priority and can be seen as the default or primary server. That means that if a request is received that does not match one of the specified ServerName directives, it will be served by this first VirtualHost.
So, it's true for my server.
The problem still remain because all virtual hosts are in folder "/etc/httpd/conf/sites-enabled" and all of them starting with 100-(sub)domain.
I've changed 100-domain in 010-domain and was great, but I want to use ISPConfig to continue to administrate that domain.
What can I do?