I use Twitter Bootstrap and Chosen beautiful drop down from long time. I never run into such problems. You could insert the selected CSS before loading the CSS or missing / overwrite the styles. Here is the full working code ...
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <link rel="stylesheet" type="text/css" href="/bootstrap/css/bootstrap.css" /> <link rel="stylesheet" type="text/css" href="/bootstrap/css/bootstrap-responsive.css" /> <title>Twitter Bootstrap + Choosen</title> <script type="text/javascript" src="//code.jquery.com/jquery-latest.js"></script> <script type="text/javascript" src="/bootstrap/js/bootstrap.js"></script> <link rel="stylesheet" type="text/css" href="/chosen/chosen.css" /> <script type="text/javascript" src="/chosen/chosen.jquery.min.js"></script> <script type="text/javascript"> $(document).ready( function() { </script> </head> <body> <div class="container"> <div class="row"> <div class="span12"> <form method="post" action="" class="form-horizontal"> <div class="control-group"> <label for="group_id" class="control-label">User Group : </label> <div class="controls"> <select name="group_id" id="group_id" class="input-xlarge"> <option value="">select...</option> <option value="1">Administrator</option> <option value="3"selected="selected">Users</option> <option value="4">Random</option> <option value="5">Super New</option> <option value="6">Famous</option> </select> </div> </div> </form> </div> </div> </div> </body> </html>
And here is the image of the attachment / screenshot (as is)

Hope this helps. Thanks!!
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