jQuery Grid Plugin - jqGrid

If multikey: option is specified, clicking in some row checkbox puts chechboxes to all rows but no one rows are selected, row background does not change. How to fix ?

grid.jqGrid({
       url: '<%= ResolveUrl("~/Grid/GetData?_entity=Strings")%>',
       scroll: 1,
       datatype: "json",
       mtype: 'POST',

       colModel: [
     { name: 'source', editable: true },
     { name: 'est', editable: true },
     { name: 'eng', editable: true },
     { name: 'rus', editable: true },
     { name: 'fin', editable: true },
     { name: 'lvl', editable: true },
     { name: 'ger', editable: true },
     { name: 'istopic', editable: true },
     { name: 'critical', editable: true },
    ],

                ondblClickRow               
                : function (id) {
                    if (id && id !== lastSel) {
                        grid.restoreRow(lastSel);
                        lastSel = id;
                    }
                    grid.editRow(id, true);

                },
                rowNum: 100,
                autoencode: true,
                gridview: true,
                pager: '#pscrolling',
                sortname: 'est',
                viewrecords: true,
                sortorder: "asc",
                caption: "Test",
                rowList: [100, 1000, 100000],
                editurl: '<%= ResolveUrl("~/Grid/Save?_entity=Strings")%>',
                multikey: "ctrlKey",
                multiselect: true
            });