[Exim] force a router to loop

hi,

Thanks to Nico Erfurth, i can force exim to loop in a router prefixing the mail
address with a hash

But I still dont understand why this router doesnt loop infinitly :

loop:
driver = redirect
data = $local_part@$domain
repeat_use = true
check_ancestor = false
redirect_router = loop

is there something i didnt understand about check_ancestor and repeat_use ?

thanks

Edouard