Firing an analytics event on a link or form which changes the page sometimes causes the analytics event to be canceled. The proper way to handle this is to use a callback function like below.

tracking.js

var that = this;
event.preventDefault();
var callback = function() {
	$(that).parents('#nl_form').submit();
}
_gaq.push(['_set','hitCallback', callback]);
_gaq.push(['_trackEvent', 'Newsletter Subscription', 'Started', window.location.pathname]);