Jqgrid remove blank header cell after last column

There is strange behavior in my jqgrid. I suddenly noticed that there is a blank header cell after my last column and I want to get rid of it. Any idea how?

Here is the definition for my jqgrid:

myGrid.jqGrid({
    colNames: ['Order Id', 'a', b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
      j', 'k', 'l', 'm'],
    colModel: [
      { name: 'OrderId', index: 'OrderId', width: 58, editable: false, align: 'center' },
      { name: 'a', index: 'a', width: 68, editable: false, align: 'center', sortable: false },
      { name: 'b', index: 'b', width: 43, editable: false, align: 'center', sortable: false },
      { name: 'c', index: 'c', width: 48, editable: false, align: 'center', sortable: false },
      { name: 'd', index: 'd', width: 63, editable: false, align: 'center', sortable: false },
      { name: 'e', index: 'e', width: 123, editable: false, align: 'center', sortable: false },
      { name: 'f', index: 'f', width: 73, editable: false, align: 'center', sortable: false },
      { name: 'g', index: 'g', width: 123, editable: false, align: 'center', sortable: false },
      { name: 'h', index: 'h', width: 73, editable: false, align: 'center', sortable: false },
      { name: 'i', index: 'i', width: 78, editable: false, align: 'center', sortable: false },
      { name: 'j', index: 'j', width: 117, editable: false, align: 'center', sortable: false },
      { name: 'k', index: 'k', width: 53, editable: false, align: 'center', sortable: false },
      { name: 'l', index: 'l', width: 73, editable: false, align: 'center', sortable: false},
      { name: 'm', index: 'm', width: 43, editable: false, align: 'center', sortable: false}        ],
    pginput: false,
    pgbuttons: false,
    hidegrid: false,
    pager: '#divPager',
    gridview: true,
    rownumbers: true,
    rownumWidth: 20,
    caption: 'Trading Positions',
    loadonce: true,
    viewrecords: true,
    recordtext: "",
    emptyrecords: "No trading positions to display",
    shrinkToFit: false
  });