BIND 9.3.2 on FreeBSD 6.1 out of control

[patrick]

I'm running BIND 9.3.2 on FreeBSD 6.1, and am noticing that it gets
out of control after running for a while.

  PID    UID           THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
60480     53             1 132    0   195M   194M RUN     41.7H 75.54% named

After restarting it, its CPU usage goes back down to what it should
be, as does its memory usage. I really don't want to babysit this
process, so I'm trying to find the cause of this. I have
"max-cache-size" set to "150M", as before I turned this on, this
process would just grow and grow until it hit FreeBSD's limit and
would stop responding all together not to mention eating up as much
CPU time as it could.

I never had this problem at all with BIND 8, and am wondering if
there's something I'm doing wrong with BIND 9 to have this problem?
Has anyone else experienced this? On a related note, is there any way
to have BIND 9 keep its memory usage much lower automatically without
having to set an arbitrary/explicit max-cache-size? (ie. Have it clean
up its own cache for entries that haven't been used after a certain
period of time?)

Any help would be greatly appreciated.

Patrick