Code in main.js
is throwing an exception in Internet Explorer. The mapster config never gets run when this fails.
$(document).ready(function() {
Site.init();
if (($.browser.msie) && ($.browser.version <= "9.0")) {
$('input[placeholder], textarea[placeholder]').placeholder();
SCRIPT438: Object doesn't support property or method 'placeholder'
Generally speaking, to troubleshoot in IE, just hit F12 and click "Start Debugging." It will be immediately apparent if a script is failing.