with some site navigation doesn't work

With some site, navigation trough ipcop doesn't work, and connection is
refused.

ipcop connect via pppoe dsl

If I connect directly, from a computer of the same lan at the same
pppoe dsl, that site is regulary viewed

this is three link:
work always: http://www.softemedia.com/
doesn't work: http://www.smartcontroller.org/
doesn't work: http://www.automation-domotica.com

Firs site is on this IP: 80.247.73.76
2nd & 3rd site are on : 80.247.73.75

That server use Host header redirection.

Bye
Gianluca