title: jqPivot is grouping column headers that do not belong to the group
body: <p>I am trying to utilize the column header group functionality of jqgrid's jqpivot to have two column headers (A header for day of the week, and another header for the actually date).</p>
  
  <pre><code>    var crewAttendance = { "total": 1, "page": 0, "records": 7,
              "rows": [
                  { "ID": "1", "UserID": "10", "AttendanceTypeID": "6", "AttendanceDate": "04/05/15", "AttendanceDay": "SUN" },
                  { "ID": "21", "UserID": "10", "AttendanceTypeID": "12", "AttendanceDate": "04/06/15", "AttendanceDay": "MON" },
                  { "ID": "41", "UserID": "10", "AttendanceTypeID": "19", "AttendanceDate": "04/07/15", "AttendanceDay": "TUE" },
                  { "ID": "61", "UserID": "10", "AttendanceTypeID": "17", "AttendanceDate": "04/08/15", "AttendanceDay": "WED" },
                  { "ID": "81", "UserID": "10", "AttendanceTypeID": "17", "AttendanceDate": "04/09/15", "AttendanceDay": "THU" },
                  { "ID": "101", "UserID": "10", "AttendanceTypeID": "19", "AttendanceDate": "04/10/15", "AttendanceDay": "FRI" },
                  { "ID": "121", "UserID": "10", "AttendanceTypeID": "19", "AttendanceDate": "04/11/15", "AttendanceDay": "SAT" }
              ], "userID": ["10"], "firstName": ["Christopher"]
          }
          // create jqPivot Grid
      var grid = $("#pvtCrewAttendance");
      grid.jqGrid("jqPivot",
          crewAttendance.rows,
          {
              xDimension: [
                  {
                      isGroupField: false,
                      width: 70,
                      dataName: 'UserID',
                      label: 'UserID'
                  }
              ],
              yDimension: [
                  {
                      dataName: 'AttendanceDay'
                  },
                  {
                      dataName: 'AttendanceDate'
                  }
              ],
              aggregates: [
                  {
                      aggregator: 'max',
                      width: 80,
                      member: 'AttendanceTypeID',
                      summarytype: 'count',
                      sortable: true,
                      resizable: false
                  }
              ],
              groupSummary: false,
              colTotals: true
          },
      // grid options
          {
          height: 'auto',
          pager: '#nav',
          caption: 'Crew Attendance'
      });
  
      var cm = grid.getGridParam('colModel');
      for (var iCol = 0; iCol &lt; cm.length; iCol++) {
          var cmi = cm[iCol];
          if (cmi.label.length == 3 || cmi.label.length == 0 || cmi.label == '\&amp;nbsp\;') {
              grid.jqGrid('hideCol', cmi.name);
          }
      }
      grid.trigger('reloadGrid');
  </code></pre>
  
  <p>and so far it is working for SUN and MON but for some reason, jqPivot's column header grouping is not working properly for the rest of the days (TUE and WED combines, and then THU, FRI, and SAT also combines but they should not because they are at different dates). See jsFiddle <a href="https://jsfiddle.net/4en1b68c/5/" rel="nofollow">here</a></p>
  
  <p>How can I make it work for the rest of the days?</p>
  
  <p>NOTE: I cannot combine the two headers together because I am going to rotate the date by 90 degrees. I've already done this part, but removed it in the fiddle to lessen the clutter.</p>