.net - JQuery Click Disappears Into Some Abyss?

Here is my setup: I have an asp.net button on a page --

<asp:Button id="btnSelectEmp" runat="server" Text="Select Employee" />

I have a .js file with the following jQuery click event --

$("input[id$='_btnSelectEmp']").click(function ($e) {
$("div[id$='_divEmpSearch']").css("display", "inline");
$e.preventDefault();
});

As you can see, clicking upon the button will set a div visible. Nothing special; not rocket science. The div is wrapped with an asp.net update panel, and it contains an asp.net user control (.ascx)

<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<div id="divEmpSearch" runat="server" style="display: none;">[code]....

The button in the user control that does a postback is working great. I click it, a postback occurs and my div control is re-hidden. I can then click on the Select Employee button (the one that I supplied the code for at the very first of the question) and the jQuery click event is handled and the div will be reshown.However, the button in the user control that does an asynchronous postback works also, but after it hides the div, if I then click on the Select Employee button the jQuery click event will not be handled.What this tells me is that for some reason during an asynchronous postback to the page, something happens to the Select Employee button so that the jQuery click event no longer happens. Why?