Header is hidden by first row in Grid

[EToreo]

I have an Editor grid that has a problem when adding a row. After 1 second elapses the new row gets added and covers up the header row (it's there, just visually covered by the first row). Is this a bug, or am I Setting something up incorrectly?

         standardColumns: function()
         {
            return {
               Employee: {
                  field: 'Employee',
                  label: 'Employee'
               };
         },
         postCreate: function()
         {
            this.inherited(arguments);
            var cols = this.standardColumns();
            this.set("columns", cols);
            this.set("collection", new TrackableMemory({data:[]}));

            setTimeout(lang.hitch(this, function()
            {
               this.addBlankRow();
            }), 1000);
         },
         addBlankRow: function()
         {
            this.collection.put({Id: Math.random(), Employee: ''});
         }