expired cache records

[Jonathan de Boyne Pollard]

JS> I'm not sure any client would send in dynamic
JS> updates with a 1 second TTL....

Why are you not ?  People create all sorts of harebrained bodges with 
the DNS to vainly attempt to solve problems that it simply isn't the 
tool for solving.  And people do set low TTLs where there is no actual 
call for them.  Just look at the "A" resource record set for 
"www.barnesandnoble.com.", for example.  (For kicks, also try an "ANY" 
query.)

Make sure that your DNS server isn't doing exactly what it has been told 
to do first before you start looking for other explanations.