Comment 5 for bug 653132

> s-c-p falls into an unbreakable infinite loop of the credentials dialog and the dialog telling that the credentials are not correct.

This seems to be a change in behaviour for CUPS. It used to be that providing an empty string for the password from the auth callback would cancel the operation, but this no longer seems to be the case.

(e.g. try some lpadmin command... just pressing enter at the password prompt used to quit)