Aha, bad word filters
Many systems have blacklists of words when they send out those handy "enter this code" form entries. We had fun generating the list, only for an apoplectic director to come in and complain that the system, in a demo, had provided the code "UTWAT" for him to enter. Apparently this would end civilisation as we know it, destroy our reputation etc etc.
Rather than make the code generator really slow I just removed all the vowels. Still in production I think.
Biting the hand that feeds IT
