I've discovered a weird behavior when creating and deleting a hostgroup. Api user is member of Zabbix administrators user group which has permission to manipulate all hostgroups.

Error can be reproduced as shown below:

1. Create a new hostgroup
2. request
   POST /zabbix/api_jsonrpc.php HTTP/1.1
   Content-Type: application/json

{
"jsonrpc":"2.0",
"method":"hostgroup.create",
"params":[

{"name":"new_group"}

],
"auth":"780eda433f4c24b67bec89244c7976e6",
"id":3
}

1. response
   HTTP/1.1 200 OK
   Content-Length: 53
   Date: Wed, 20 Jun 2012 15:42:21 GMT
   Server: Apache/2.2.16 (Debian)
   X-Powered-By: PHP/5.3.3-7+squeeze8
   Connection: close
   Content-Type: application/json

{"jsonrpc":"2.0","result":

{"groupids":["10"]}

,"id":3}

1. Try to destroy newly created hostgroup

1. request
   POST /zabbix/api_jsonrpc.php HTTP/1.1
   Content-Type: application/json

{
"jsonrpc":"2.0",
"method":"hostgroup.delete",
"params":[

{ "groupid":10 }

],
"auth":"780eda433f4c24b67bec89244c7976e6",
"id":2
}

1. response
   HTTP/1.1 200 OK
   Content-Length: 1106
   Date: Wed, 20 Jun 2012 15:43:54 GMT
   Server: Apache/2.2.16 (Debian)
   X-Powered-By: PHP/5.3.3-7+squeeze8
   Connection: close
   Content-Type: application/json

{"jsonrpc":"2.0","error":{"code":-32500,"message":"Application error.","data":"You do not have permission to perform this operation.","debug":[

{"file":"\/opt\/share\/zabbix\/frontend\/api\/classes\/CHostGroup.php","line":715,"function":"exception","class":"CZBXAPI","type":"::","args":[120,"You do not have permission to perform this operation."]}

,{"function":"delete","class":"CHostGroup","type":"->","args":[[

{"groupid":10}

]]},{"file":"\/opt\/share\/zabbix\/frontend\/api\/rpc\/class.czbxrpc.php","line":106,"function":"call_user_func","args":[[{},"delete"],[

{"groupid":10}

]]},{"file":"\/opt\/share\/zabbix\/frontend\/api\/rpc\/class.czbxrpc.php","line":64,"function":"callAPI","class":"czbxrpc","type":"::","args":["hostgroup.delete",[

{"groupid":10}

]]},{"file":"\/opt\/share\/zabbix\/frontend\/api\/rpc\/class.cjsonrpc.php","line":66,"function":"call","class":"czbxrpc","type":"::","args":["hostgroup.delete",[

{"groupid":10}

],"780eda433f4c24b67bec89244c7976e6"]},

{"file":"\/opt\/share\/zabbix\/frontend\/api_jsonrpc.php","line":54,"function":"execute","class":"CJSONrpc","type":"->","args":[]}

]},"id":2}