Sub domains not blocked

Hi,

In the web filter, no matter what I block be that:

* wildcard

.* reg exp

or even the actual domain such as:

*google.com

The sub domain can be accessed.

Say if I block mail.domain.com, even as an explicit block people can access it. But they cannot access domain.com.

I am totally lost for ideas. HTTP or HTTPS seems to make no difference.

Any help much appreciated!!

Regards