jQuery form plugin duplicate elements after submit ajax

Question

I am using jquery form plugin for sending request to server and write some data in database. After submitting form some elements like sidebar is duplicated. I set target to be container that be refreshed after successing. All work good but whay elements id duplicated.

<div class="contaner-fluid">
 <div class="sidebar_lft"> Sidebar </div> <!-- This sidebar is dupicated -->
 <div id="main-content">
      <!-- PHP forach loop some data. This div need to been refreshed after success-->
    <form id="user-form" action="user/update" metod="post">
        <input type="text" name="username">
        <input type="submit">
    </form>
 </div>
</div>

And jquery:

$(document).ready(function(e) {
    $('#user-form').ajaxForm({
        target: '#main-content',
        success: function() {
            alert('Success');
        }
    });
});

All data is saved in database and all work good expect that reloading div. When ajax execute success callback he duplicate my sidebar idk whay.