vm.memory.size[available]/[free] counts wrong

[pirat]

Zabbix server version - 2.0 x64
Zabbix agent version - 2.0 x64

zabbix agent collect wrong free memory information. When i have about 2-3 Gb free RAM zabbix-agent counts 200-400 Mb of free RAM. For example when "free" command show this

free
total used free shared buffers cached
Mem: 4023960 618616 3405344 0 0 0
-/+ buffers/cache: 618616 3405344
Swap: 0 0 0

zabbix-agent log contains this:

--
26214:20120731:010043.308 Requested [vm.memory.size[free]]
26214:20120731:010043.308 Sending back [162091008]
26216:20120731:010043.325 Processing request.
--
26216:20120731:010112.108 Requested [vm.memory.size[available]]
26216:20120731:010112.108 Sending back [178880512]
26214:20120731:010112.113 Processing request.
--
26214:20120731:010113.128 Requested [vm.memory.size[free]]
26214:20120731:010113.128 Sending back [60952576]
26212:20120731:010113.876 In update_cpustats()
--
26214:20120731:010143.451 Requested [vm.memory.size[free]]
26214:20120731:010143.451 Sending back [54202368]
26216:20120731:010143.457 Processing request.
--
26214:20120731:010212.783 Requested [vm.memory.size[available]]
26214:20120731:010212.783 Sending back [135208960]
26212:20120731:010213.341 In update_cpustats()
--
26214:20120731:010213.807 Requested [vm.memory.size[free]]
26214:20120731:010213.807 Sending back [61349888]
26212:20120731:010214.343 In update_cpustats()

Please help to understand and to fix this. Thanks.