leech will change my current account to another user

I did the following steps:
0.Login as the super user (uid=0)
1.Create a content type called blogger with only two fileds(title & body) by CCK.
2.Create a new node (content type : blogger),and then create a node template.
3.Enable the leech function in the content type of blogger.
4.Create a new node(blogger),give an URL for leech,and change the author to another account named john.
5.view the node and click "leach now".
6.It returns a blank page,and I go back to the previous page(enter backspace),the account changed to john.
I have not tested if I am not a super user , if I am not and the the above tricks will also work , It is terrible.