Input error: Invalid referer

[borizz]

I left an hour trying to register an account on this forum.

It functions almost fully, but does not show captcha with the message "Input error: Invalid referer" in verification field.

Finally I found out that google refers forum topics by IP (something like http://195.74.76.34/index.php?action=register, while it should be http://forum.avast.com/index.php?action=register ) and forum does not redirect you to register page specified by DNS.