default index page problem

[pawan]

of late, if a site is pointed to ispconfig server(in DNS record of domain registrar), instead of showing the default index page, as it used to show, now I am getting one of the website as default(if no domain is created for the domain in question).

Example:
a new domain example.com is registered and its A record is pointed to the ip of my ISPCONFIG server, but no domain is created in ISPCONFIG control panel than when browsing that domain used to show a default ISPCONFIG index page, but don't know from when, but now it is showing one of the sites from my server.

Your help is needed to address this problem.
Thanks.