dnscache querying wrong (old?) NS sometimes

Hi there, from time to time dnscache seems to be querying a wrong NS to
resolve a domain, and doing it again and again after the old NS record
expires. It starts querying the correct NS only after I restart it by
running "svc -t /var/service/dnscache". Hint: all such NS records have
been "out-of-bailiwick" domains, in DJB's parlance, both wrong (old?)
and correct, but I'm not sure it's related. The only patch differing my
setup from the vanilla djbdns is DUMPCACHE, which I currently don't use
anyway due to very heavy use of RAM when initializing (i.e. I moved away
DUMPCACHE, DUMPCACHETMP & SLURPCACHE).

BIND 9 doesn't seem to have this issue.

Anyone knows what's wrong? Thanks.