jqGrid - 'in' op filter not working

$(document).ready(function() {

    var testScores = {
        testScore: [
        {
            student: 'Alex',
            score: 50,
            grade: 10
        },
        {
            student: 'Alice',
            score: 77,
            grade: 10
        },
        {
            student: 'Barbara',
            score: 60,
            grade: 11
        },
        {
            student: 'Bonnie',
            score: 73,
            grade: 10
        },
        {
            student: 'Charlie',
            score: 71,
            grade: 10
        },
        {
            student: 'Cory',
            score: 75,
            grade: 11
        },
        {
            student: 'David',
            score: 80,
            grade: 11
        },
        {
            student: 'Don',
            score: 83,
            grade: 11
        },
        {
            student: 'Elizabeth',
            score: 90,
            grade: 12
        },
        {
            student: 'Evelyn',
            score: 100,
            grade: 12
        },
        {
            student: 'Fisk',
            score: 83,
            grade: 9
        },
        {
            student: 'Fred',
            score: 100,
            grade: 9
        }
        ]
    };

    var myfilter = {
        groupOp: "AND",
        rules: [
            {field: 'score', op: 'gt', data: 70},
            //{field: 'grade', op: 'in', data: [10, 11, 12]}
        ]
    };

    var grid = $('#scores').jqGrid({
        datatype: 'local',
        colNames: ['Name', 'Grade', 'Score'],
        colModel: [
        {
            name: 'student',
            index: 'student',
            sorttype: 'int',
            width: 150
        },
        {
            name: 'grade',
            index: 'grade',
            sorttype: 'int',
            width: 150,
        },
        {
            name: 'score',
            index: 'score',
            sorttype: 'int',
            width: 150
        }
        ],
        data: testScores.testScore,
        autowidth: 'true',
        height: '100%',
        pager: '#pager',
        sortname: 'score',
        sortorder: 'desc',
        viewrecords: true,
        grouping: true,
        groupingView: {
            groupField: ['grade'],
            groupColumnShow: [true],
            groupText: ['Grade {0} - {1} students'],
            groupCollapse: 'true',
            groupOrder: 'desc'
        },
        caption: 'Test Scores',
        search: true,
        postData: {
            filters: JSON.stringify(myfilter)
        }
    });
});