why can't my account be used at wiki.postgresql.org after having registered in www.postgresql.org?

Hi,
  I just registered my acount using this url: https://www.postgresql.org/account/signup/, then i use the new account to login www.postgresql.org, everything works well.
  But when I try to login wiki.postgresql.org using the same account, i got an error: There is no user by the name "myaccount". Check your spelling.
  Yet another page for registering at wiki.postgresql.org, named http://wiki.postgresql.org/wiki/Special:UserLogin/signup, tells me i can't signup a new account for wiki.
  how to register an acount for wiki.postgresql.org?
  Thanks!
oebg