Trouble with NAMED BIND 9.3.2-P1

[DR]

Named grows up in memory (over 850 mb) to its limit and begin very
slow response (over 1000 ms) to client and after some time - stop
response.
rndc stop - doesn't work, only kill -9.

named.conf
options{
        max-cache-size 640M;
        max-cache-ttl 32400;
        max-ncache-ttl 3600;
        cleaning-interval 30;
        recursive-clients 1200;

}

rndc status

number of zones: 2736
debug level: 0
xfers running: 1
xfers deferred: 0
soa queries in progress: 33
query logging is OFF
recursive clients: 309/1200
tcp clients: 2/100
server is up and running


Named from distribution, ports, src - doesn't matter.
FreeBSD 5.5-STABLE (2 weeks ago).