icmp in ip_conntrack not seen

Hello!

I 've got a problem with my linux box, description:

Box setup:
1. Linux kernel 2.6.15 vanilla from www.kernel.org, no additional patches. 2.

# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_icmp_timeout
30
3. 
zcat /proc/config.gz |grep IP_NF
CONFIG_IP_NF_CONNTRACK=y
CONFIG_IP_NF_CT_ACCT=y
CONFIG_IP_NF_CONNTRACK_MARK=y
CONFIG_IP_NF_CONNTRACK_EVENTS=y
# CONFIG_IP_NF_CT_PROTO_SCTP is not set
CONFIG_IP_NF_FTP=y
... etc

Problem:
When pinging from other server, this box has no icmp records
in /proc/net/ip_conntrack. When pinging from this box other server those entries not exist too. Ping works ok, request/replies goes both sides (seen at tcpdump on both systems).

Those entries appear only for small time when pinging in such way: ping -f ... :-( And only one way to get them is this script:
while true;do grep icmp /proc/net/ip_conntrack;done

P.S. I think that problem exist because i set CONFIG_IP_NF_CT_ACCT option, am i wrong?
P.P.S. I can't subscribe to this list from my mail at mail.ru server, no notification about cause of this has been received, no rules at www.netfilter.org describe problems with free mail servers :-(

Best regards, Oleg