jQuery Mobile: Injected content appears then disappears immediately - jquery-mobile

Question

I have a login page using jQuery Mobile which contains the following code:
<div id="loginPage" data-role="page" data-theme="a">
<div data-role="content">
<div id="alerts"></div>
<form id="login-form">
<input type="text" id="username" name="username" value="" placeholder="username or email" />
<input type="password" id="password" name="password" value="" placeholder="password" />
<button id="login-button" onClick="userLogin()">Login</button>
</form>
</div><!-- /content -->
</div><!-- /page -->
Here is a part of my javascript that is called when the user clicks the 'Login' button. If one of the fields is left blank, I see the following text injected into the #alerts div, but then within a fraction of a second the content has disappeared again.
if (username.length == 0 || password.length == 0) {
//alert('Please enter your username or email and your password');
$('#alerts').html('Please enter your username or email and your password.').trigger('create');
}
I also tried this using .append() instead of .html(). Same result with both. I've commented out my test alert(), which works when one of the fields is left blank.
What can I do to make sure the content remains on the page once it is injected?
Thank you for any help or insight you can offer! -Mark
Per Jasper's request, here is all of the javascript that is executed when the 'Login' button is clicked:
function userLogin() {
var username = $("#username").val();
var password = $("#password").val();
if (username.length == 0 || password.length == 0) {
$('#alerts').append('Please enter your username or email and your password.').trigger('create');
}
else {
$.post("services/user-status.php", { type: 'login', username: username, password: password },
function(data) {
var response = data.item;
console.log(response);
if (response.loggedIn == false) {
$('#alerts').html('The username/email and password you used did not work. Please try again.').trigger('create');
}
else {
localStorage.userID = response.userID;
localStorage.username = response.username;
localStorage.userStatus = 'loggedIn';
$.mobile.changePage('profile.html');
}
},'json');
}
}

Answer 1

It looks like you need to stop the propagation of the click event from firing for your button. You can do that by returning false in the click event handler:
HTML --
<button id="login-button" onClick="return userLogin()">Login</button>
JS --
function userLogin() {
...
return false;
}​
Here is a demo: http://jsfiddle.net/BkMEB/3/
Also, since you are using jQuery, you can bind to the <button> element like this:
$('#login-button').bind('click', userLogin);
This is the same as putting onClick="return userLogin()" as an attribute of the button but allows you to remove your inline JS.
Here is a demo: http://jsfiddle.net/BkMEB/4/