Thanks Charly. I found this code in the last reply:
<head>
<br />
<meta http-equiv="refresh" content="0;url=http://www.afro-pfingsten.ch">
<br />
</head>
but out of "code" tags. I think it is a security hole for visitors who read contribs forum, because any one can make a redirection to an infected page or something similar.
It is justify to post a bug in bugzilla? mmm...I am sure your answer is "YES"

Maybe disabling html code in the forum are ok.
Thank you for your reply.