Redactor file upload not working

If I go to upload a file within Redactor, the upload pop-up appears, and the file does upload to resources.

However, it does not link up right within the editor and the HTML from the file upload pop-up ends up being inserted into the content HTML, and this is repeated if uploading multiple files. It is very strange.

Here's the short diagnostic report (some paths altered slightly for privacy):

    Perch: 2.8.4, PHP: 5.5.20, MySQL: 5.1.73, with PDO
    Server OS: Linux, cgi-fcgi
    Installed apps: content (2.8.4), assets (2.8.4), categories (2.8.4)
    App runtimes: <?php $apps_list = array( 'content', 'categories', );
    PERCH_LOGINPATH: /perch
    PERCH_PATH: /var/www/vhosts/x/webspace/httpdocs/perch
    PERCH_CORE: /var/www/vhosts/x/webspace/httpdocs/perch/core
    PERCH_RESFILEPATH: /var/www/vhosts/x/webspace/httpdocs/perch/resources
    Image manipulation: GD Imagick
    PHP limits: Max upload 32M, Max POST 32M, Memory: 256M, Total max file upload: 32M
    Resource folder writeable: Yes
    DOCUMENT_ROOT: /var/www/vhosts/x/webspace/httpdocs
    REQUEST_URI: /perch/core/settings/diagnostics/
    SCRIPT_NAME: /perch/core/settings/diagnostics/index.php

Here's the code that gets inserted within the Redactor HTML

<div style="display: none; height: 1142px;" class="asset-chooser">
    <div class="asset-topbar">
        <div class="actions">
            <a href="#" class="close icon asset-icon"><span class="hidden">Close</span></a>
            <a href="#" class="add button">Add Asset</a>
            <a href="#" class="select button">Use Selected</a>
        </div>
        <h2>Select an Asset</h2>
    </div>
    <div class="asset-drop">
        <form action="/mificms/core/apps/assets/upload/" id="asset-dropzone" method="post" enctype="multipart/form-data">
            <div class="fallback">
                <input name="file" multiple="" type="file">
                <input value="Upload" type="submit">
            </div>
        </form>
    </div>
    <div class="asset-field">
        <div id="asset-filter" class="asset-filter">
        </div>
        <div style="position: relative; overflow: hidden; width: auto; height: 696px;" class="slimScrollDiv">
            <div style="overflow: hidden; width: auto; height: 696px;" class="inner">
            </div>
            <div style="background: none repeat scroll 0% 0% rgb(0, 0, 0); width: 7px; position: absolute; top: 0px; opacity: 0.4; display: block; border-radius: 7px; z-index: 99; right: 1px;" class="slimScrollBar">
            </div>
            <div style="width: 7px; height: 100%; position: absolute; top: 0px; display: block; border-radius: 7px; background: none repeat scroll 0% 0% rgb(51, 51, 51); opacity: 0.2; z-index: 90; right: 1px;" class="slimScrollRail">
            </div>
        </div>
    </div>
</div>