JQGrid problem with tabs and frozen columns

two grids in jqueryui tabs, if using frozen columns the headers on the hidden tab are overwritten by the first row of data.

by danypd69

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.9.2/themes/base/jquery-ui.css">
<link rel="stylesheet" href="http://trirand.com/blog/jqgrid/themes/ui.jqgrid.css">
<script src="http://trirand.com/blog/jqgrid/js/i18n/grid.locale-en.js"></script>
<script src="http://trirand.com/blog/jqgrid/js/jquery.jqGrid.min.js"></script>
<div id="tabs">
	<ul>
		<li><a href="#tab1">Grid 1</a></li>
		<li><a href="#tab2">Grid 2</a></li>
	</ul>
	<div id="tab1">
		<table id="grid1"></table>
	</div>
	<div id="tab2">
		<table id="grid2"></table>
	</div>
</div>

JavaScript

$(document).ready(function () {
			$("#tabs").tabs();
			$("#grid1").jqGrid({
				datatype: 'local',
				colNames: ['Header1', 'Header2', 'nf1', 'nf2', 'nf3', 'nf4', 'nf5', 'nf6'],
				colModel: [
					{ 'name': 'frozen1', width: 50, frozen: true},
					{ 'name': 'frozen2', width: 50, frozen: true},
					{ 'name': 'nf1', width: 80},
					{ 'name': 'nf2', width: 80},
					{ 'name': 'nf3', width: 80},
					{ 'name': 'nf4', width: 80},
					{ 'name': 'nf5', width: 80},
					{ 'name': 'nf6', width: 80}
				],
				width: 400,
				height: 200,
				shrinkToFit: false
			});
			$("#grid1").jqGrid('setFrozenColumns');
			fillGrid("#grid1");
			$("#grid2").jqGrid({
				datatype: 'local',
				colNames: ['Header1', 'Header2', 'nf1', 'nf2', 'nf3', 'nf4', 'nf5', 'nf6'],
				colModel: [
					{ 'name': 'frozen1', width: 50, frozen: true},
					{ 'name': 'frozen2', width: 50, frozen: true},
					{ 'name': 'nf1', width: 80},
					{ 'name': 'nf2', width: 80},
					{ 'name': 'nf3', width: 80},
					{ 'name': 'nf4', width: 80},
					{ 'name': 'nf5', width: 80},
					{ 'name': 'nf6', width: 80}
				],
				width: 400,
				height: 200,
				shrinkToFit: false
			});
			$("#grid2").jqGrid('setFrozenColumns');
			fillGrid("#grid2");
		});
		function fillGrid(id) {
			for (var idx = 1; idx < 10; idx++) {
				$(id).jqGrid("addRowData", idx, { frozen1: 'Frozen1', frozen2: 'Frozen2', nf1: 'Free1', nf2: 'Free2', nf3: 'Free3'});
			}
		}