* I can't get right result number when using IFX_AFFECTED_ROWS() ! *

Following is my configure and source code
-----------------------------------------
DB name    : test
TABLE name : test
DB user    : informix (pass:*****)

Schema file
---
{ TABLE "informix".test row size = 119 number of columns = 4 index size = 12 }
create table "informix".test 
  (
    id serial not null ,
    name nchar(8) not null ,
    email nvarchar(50,50),
    comment text,
    primary key (id)  constraint "informix".priid
  ) extent size 16 next size 16 lock mode row;
revoke all on "informix".test from "public";
---

PHP Source Code
---
<?
$conn_id = ifx_connect("test@linux","informix","****");
ifx_textasvarchar(1);
$query = "select * from test";
$res_id = ifx_query($query,$conn_id);
$rowcount = ifx_affected_rows($res_id);
echo($rowcount);
?>
---
--------------------------------------------

I'm insert 5 rows into test table.
But $rowcount's value is 10

I'm insert 13 rows into test table.
But $rowcount's value is 10

Alaways $rowcount's value is 10

I can't find my mistake.
How can I solve problems.


Thanks.