jqGrid randomly checks checkbox column

I am using jqGrid for converting Json object into regular HTML table. From server I get object and everything is good except one thing. I have added one column that is actually checkbox column. In value attribute of each checkbox input I've put ID that later I am passing back to server if checkbox is checked.

$("#membersGrid").jqGrid({
    url: '/Member/GetAllMembers',
    mtype: "GET",
    styleUI: 'Bootstrap',
    datatype: "json",
    colModel: [
        { label: 'Full Name', name: 'fullName', width: 150 },
        {
            label: 'Select', editable: true, name: 'id',
            edittype: 'checkbox', editoptions: { value: "true:false", defaultValue: "false" },
            formatter: "checkbox", formatoptions: { disabled: false }, width: 45
        }
    ],
    viewrecords: true,
    height: 250,
    width: 640,
    rowNum: -1,
    ajaxSubgridOptions: { async: false },
});

When generating checkbox column for value I am defining true or false and with defaultValue I wanted to state that false(unchecked) is default value for each and every generated cell with checkbox.

But instead I am getting randomly checked check-boxes:

When I inspect element in Chrome, unchecked type is auto generated in this way:

<td role="gridcell" style="" title="" aria-describedby="membersGrid_id">
     <input type="checkbox" value="400" offval="no">
</td>

And checked type like this:

<td role="gridcell" style="" title="" aria-describedby="membersGrid_id">
    <input type="checkbox" checked="checked" value="399" offval="no">
</td>

Is there some other way to tell jqGrid to avoid checking checkboxes reather that using defaultValue attribute? Or I am doing something wrongly?