Trouble with NAMED BIND 9.3.x

[User]

Named grows up in memory (over 850 mb) to its limit and begin very slow response (over 500-1000 ms) to client on same queries and after some time - stop response. rndc stop - doesn't work, only kill -9.

max-cache-size - was 256, 512, 1024 - has influence only BIND life time.

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: 739/1200
tcp clients: 2/100
server is up and running


Named from distribution, ports, src - doesn't matter.
FreeBSD 5.5-STABLE (2 weeks ago). Kernel support processes over 1 gb.