Unable to upload specific .zip file type via frontend in WordPress 4.0

I allow uploading a selected few types of files from the frontend, e.g. .zip, .mp4, .jpeg and .pdf. Till now all these file types had no issues getting attached to the post it is uploaded to. However after upgrading to WordPress 4.0, I have not been able to upload specific .zip file type from the frontend, although it uploads well from the backend using media-upload interface. Please note that the other file types .mp4 and .pdf files still attach with no issues.

Given below is the entire code that performs the attachment function.

if ( isset( $_POST['upload_attachments'] ) && $_SERVER['REQUEST_METHOD'] === 'POST' && wp_verify_nonce($_POST['secure_upload'], 'upload_attachments_nonce')) {

    //checking if upload is empty
    //checking if universal filesize is valid

    if ($_FILES) { //loop through multiple files.         
        $files = $_FILES['upload'];
        foreach ($files['name'] as $key => $value) {
            if ($files['name'][$key]) {
                $file = array(
                    'name'     => $files['name'][$key],
                    'type'     => $files['type'][$key],
                    'tmp_name' => $files['tmp_name'][$key],
                    'error'    => $files['error'][$key],
                    'size'     => $files['size'][$key]
                );

                $uploaded_file_type = $files['type'][$key];
                $allowed_file_types = array('image/jpg', 'image/jpeg', 'image/png', 'application/pdf', 'application/zip', 'video/mp4');
                $uploaded_file_size = $files['size'][$key];
                $size_in_kb = $uploaded_file_size / 1024;
                $file_size_limit = 10000; // Your Filesize in KB


                if(in_array($uploaded_file_type,  $allowed_file_types)) { 
                   if( $size_in_kb > $file_size_limit ) {
                   $upload_error .= 'Image files must be smaller than '.$file_size_limit.'KB';
                   return;
                   } else {
                   $_FILES = array("upload" => $file);
                   foreach ($_FILES as $file => $array) {
                   $newupload = insert_attachment($file,$post_id);
                   //return; this loop neds to run multiple times so no return here
                 }      
                 }
                 } else { $upload_error .= 'Invalid File type';
                         return;
                        }                                                              

                }
            }
        }                  

    header ('Location: ' . $_SERVER['REQUEST_URI']);//Post, redirect and get
    exit();
    }//end of nonce check 

Helper function insert_attachment by goldenapples

function insert_attachment($file_handler,$post_id,$setthumb='false') {

    // check to make sure its a successful upload
    if ($_FILES[$file_handler]['error'] !== UPLOAD_ERR_OK) __return_false();

    require_once(ABSPATH . "wp-admin" . '/includes/image.php');
    require_once(ABSPATH . "wp-admin" . '/includes/file.php');
    require_once(ABSPATH . "wp-admin" . '/includes/media.php');

    $attach_id = media_handle_upload( $file_handler, $post_id );

    //if ($setthumb) update_post_meta($post_id,'_thumbnail_id',$attach_id);
    return $attach_id;
}

Form Html

<form method="post" id="frontend-attachment-upload-form" action="" enctype="multipart/form-data" >
<input type="file" multiple="true" name="upload[]">   

<?php wp_nonce_field('upload_attachments_nonce','secure_upload'); ?>
<input type="submit" id="upload_attachments_button" name="upload_attachments" value="UPLOAD">
<form>

The .zip file is not getting uploaded at all, otherwise I would find them in media-library ,even if unattached. When I try to upload a .zip file in the frontend, it simply returns the error invalid file type. As you can see this line clearly defines all file types:

$allowed_file_types = array('image/jpg', 'image/jpeg', 'image/png', 'application/pdf', 'application/zip', 'video/mp4');

So how come the .mp4, .pdf, .jpeg all other file types gets attached fine and .zip does not? Logically, If there was a mistake in the loop, no file-types would be uploaded at all. Also the fact is .zip files had been uploading fine till a few days ago. I am clueless to what is happening. A little help will be appreciated please.

Just in case I checked for allowed file types and it lists .zip file type as allowed. So, is it possible that wordpress might have made some changes in image.php or file.php or media.php that would block specific file types to be uploaded in the frontend ?

<?php $allowed_mimes = get_allowed_mime_types();
        echo '<pre>';
        print_r($allowed_mimes);
        echo '</pre>';
        ?>

UPDATE : This issue has been solved, kindly take a look at the accepted answer.

*I thought I will write this as an update but then I thought it is better to provide the solution as an answer because someone may skip the solution in the question update.

There is no mistake in my code or in the loop for that matter. This is not a server misconfiguration either. As a part of debugging I was echoing back the uploaded filetypes and I realized that when I upload a .zip file it returns as application/x-zip-compressed instead of what I thought should be application/zip. So a small change in the code did the job.

$allowed_file_types = array('application/x-zip-compressed', 'other file types......');

Above works fine now, also to note the .rar file has to be application/x-rar-compressed. I wish it was mentioned on the relevant codex page. I am still sure that this is something that came along with wordpress 4.0. Thanks to @ialocin and @aifrim and others for help.