[bug] ListGrid with groupByField is always Grouping... then changing focus in filters

[antanas.arvasevicius]

Hi,
If I use a listgrid with groupByField and filterByCell is enabled then in any focus in filter section will trigger "Grouping..." dialog, and listgrid flickers.

steps:
1) focus on "id" filter
2) focus on "group field" filter
3) focus on "some_other" filter

Result:
every time it will flicks and shows "Grouping.." dialog

Expected:
nothing happens, only regroup should happen then fetch from server is necessary.

    var testData = new Array(500).map(function (v, i) {
        return {id: "" + (i + 1), groupField: "" + (i % 10) + 1}
    });

    isc.DataSource.create({
        ID: "ds",
        clientOnly: true,
        fields: [{name: 'id', primaryKey: true}, {name: 'groupField', type: 'text'}],
        testData: testData,
        fetchData: function (criteria, callback, requestProperties) {
            console.log('fetchData: ', criteria, requestProperties);
            this.performDSOperation("fetch", criteria, callback, requestProperties);
        }
    });

    isc.ListGrid.create({
        groupByField: ["groupField"],
        width: 400,
        height: 200,
        autoDraw: true,
        dataSource: "ds",
        autoFetchData: true,
        useAllDataSourceFields: false,
        showFilterEditor: true,
        filterByCell: true,
        fields: [
            {
                name: 'id'
            },
            {
                name: 'groupField'
            },
            {
                name: 'some_other'
            }
        ]
    });