$_POST Variable Empty in Quercus Portlet on Liferay 6

Question

My company is migrating from Luminis 5.1 to Luminis 5.3 (both built from Liferay 6), and we're running into a problem where portlets that POSTed fine in 5.1 no longer supply the Post Body in 5.3.

For example, this form

<form id="duplication-request" class="form-horizontal" method="post" enctype="multipart/form-data" action="index.php">

    <fieldset>
        <legend>General Information</legend>

        <div class="form-group">
            <label for="name" class="col-sm-4 control-label">Name</label>
            <div class="col-sm-8">
                <input type="text" id="name" class="form-control" name="name"
                       value="<?= $input->request->get('name', $name) ?>" required>
            </div>
        </div>
    </fieldset>

    <button class="btn btn-primary">Submit</button>
</form>

would supply the $_POST['name'] variable just fine in Luminis 5.1, but in 5.3, not even the 'name' index is registered.

If I serve it locally via php -S 0.0.0.0:8080, the $_POST['name'] variable is registered correctly, leading me to think it's a problem with Quercus (which, unfortunately, isn't well supported)

Are there any settings in web.xml that I need to turn on in order to get Luminis to proxy the Request Body into Quercus so PHP can work with it?