here are all necessary info, i think i should say anything else:

this is a global host with 38 zones (on all are the zabbix agent 1.8.4 installed)
root@at2f1uivsh104:~# uname -X
System = SunOS
Node = at2f1uivsh104
Release = 5.10
KernelID = Generic_142909-17
Machine = sun4u
BusType = <unknown>
Serial = <unknown>
Users = <unknown>
OEM# = 0
Origin# = 1
NumCPU = 64

root@at2f1uivsh104:~# prtdiag | head
System Configuration: Sun Microsystems sun4u Sun SPARC Enterprise M5000 Server
System clock frequency: 1012 MHz
Memory size: 262144 Megabytes

root@at2f1uivsh104:~# prstat -L
PID USERNAME SIZE RSS STATE PRI NICE TIME CPU PROCESS/LWPID
22369 zabbix 12M 7792K cpu61 57 5 60:56:57 1,5% zabbix_agentd/1
7646 zabbix 11M 5928K cpu5 49 5 56:41:22 1,4% zabbix_agentd/1
8274 zabbix 11M 5776K cpu28 46 5 56:49:24 1,4% zabbix_agentd/1
8404 zabbix 11M 5952K cpu27 29 5 56:53:12 1,4% zabbix_agentd/1
8249 zabbix 11M 5648K cpu8 38 5 56:49:11 1,4% zabbix_agentd/1
8331 zabbix 11M 5784K cpu46 16 5 56:16:19 1,4% zabbix_agentd/1
7942 zabbix 11M 5688K cpu26 26 5 56:43:50 1,4% zabbix_agentd/1
8233 zabbix 11M 5952K cpu43 21 5 56:50:03 1,4% zabbix_agentd/1
8385 zabbix 11M 5840K cpu24 40 5 56:50:54 1,4% zabbix_agentd/1
8360 zabbix 11M 5952K cpu1 47 5 56:53:31 1,4% zabbix_agentd/1
8174 zabbix 11M 5736K sleep 37 5 56:45:56 1,4% zabbix_agentd/1
7893 zabbix 11M 5936K cpu29 47 5 56:43:08 1,4% zabbix_agentd/1
7685 zabbix 11M 5936K cpu21 44 5 56:40:34 1,4% zabbix_agentd/1
7586 zabbix 11M 5808K cpu7 52 5 56:40:56 1,4% zabbix_agentd/1
7963 zabbix 11M 5696K cpu9 57 5 57:01:49 1,4% zabbix_agentd/1
8068 zabbix 11M 5680K cpu42 48 5 56:14:43 1,4% zabbix_agentd/1
8206 zabbix 11M 5936K sleep 43 5 56:48:02 1,4% zabbix_agentd/1
7880 zabbix 11M 5736K cpu44 46 5 56:12:09 1,4% zabbix_agentd/1
7568 zabbix 11M 5808K cpu10 41 5 56:37:32 1,4% zabbix_agentd/1
8019 zabbix 11M 5688K cpu11 50 5 56:46:58 1,4% zabbix_agentd/1
7961 zabbix 11M 5736K cpu37 49 5 56:07:18 1,4% zabbix_agentd/1
7910 zabbix 11M 5936K cpu40 40 5 56:11:15 1,3% zabbix_agentd/1
7804 zabbix 11M 5696K cpu16 8 5 56:42:40 1,3% zabbix_agentd/1
8027 zabbix 11M 5696K cpu4 43 5 56:48:04 1,3% zabbix_agentd/1
7730 zabbix 11M 5720K cpu47 49 5 56:10:59 1,3% zabbix_agentd/1
7671 zabbix 11M 5760K cpu35 50 5 56:08:25 1,3% zabbix_agentd/1
7863 zabbix 11M 5936K cpu20 46 5 56:41:50 1,3% zabbix_agentd/1
8312 zabbix 11M 5744K cpu12 44 5 56:48:56 1,3% zabbix_agentd/1
7606 zabbix 11M 5816K cpu14 48 5 56:41:09 1,3% zabbix_agentd/1
8369 zabbix 11M 5800K cpu32 50 5 56:19:07 1,3% zabbix_agentd/1
7926 zabbix 11M 5936K cpu3 31 5 56:43:02 1,3% zabbix_agentd/1
8394 zabbix 11M 5936K cpu38 38 5 56:20:29 1,3% zabbix_agentd/1
7630 zabbix 11M 5872K cpu36 36 5 56:06:02 1,3% zabbix_agentd/1
7808 zabbix 11M 5960K cpu41 52 5 56:12:11 1,3% zabbix_agentd/1
7758 zabbix 11M 5776K cpu33 41 5 55:31:13 1,3% zabbix_agentd/1
7998 zabbix 11M 5712K cpu34 44 5 56:12:29 1,3% zabbix_agentd/1
7713 zabbix 11M 5720K sleep 21 5 56:09:36 1,3% zabbix_agentd/1
8190 zabbix 11M 5776K cpu19 49 5 56:47:01 1,3% zabbix_agentd/1
717 root 4128K 3208K cpu59 29 0 155:16:02 1,2% in.routed/1
26212 root 87M 86M cpu62 14 0 0:00:24 1,0% xvmluinfo/1
6874 root 193M 190M sleep 52 0 74:11:50 0,6% java/3
26964 zabbix 3920K 2648K cpu45 7 5 0:00:05 0,3% mpstat/1
24782 oracle 4219M 1012M sleep 1 0 20:16:19 0,3% oracle/1
10115 root 11M 9704K cpu56 35 0 101:56:30 0,1% syslogd/10
27156 zabbix 3920K 2696K cpu31 43 5 0:00:01 0,1% mpstat/1
909 root 12M 9264K sleep 46 0 2:05:09 0,1% snmpd/1
Total: 1913 processes, 11313 lwps, load averages: 76,24, 75,72, 75,24

i have seen the same problem with agent 1.8.3.