Image assets assigned to categories are being deleted

I've created a category template which contains an image field. It seems that after a few days, the image assets that are uploaded through this template are being erased. Here's the template:

<perch:before><ul></perch:before>
<li style="margin-left: <perch:category id="catDepth" type="hidden" />0px;">
    <h4><perch:category id="catTitle" type="smarttext" label="Title" required="true" /></h4>
    <perch:category id="catSlug" type="slug" for="catTitle" suppress="true" />
    <perch:category type="color" id="color" required="true" label="Color" />
    <perch:category type="image" id="image" label="Image" width="500" help="Please use transparent PNG format" bucket="Briefing Icons" />
</li>
<perch:after></ul></perch:after>

This is on Perch 2.8.6, though I didn't see anything related mentioned in the latest update notes. Diagnostics:

Perch: 2.8.6, PHP: 5.4.24, MySQL: mysqlnd 5.0.10 - 20111026 - $Id: 2d8f599f49e5e8d2f5ba7112b5c444b3e2e48cdf $, with PDO
Server OS: Linux, litespeed
Installed apps: content (2.8.6), assets (2.8.6), categories (2.8.6), perch_blog (4.6), perch_forms (1.8.3)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_forms', 'perch_blog' );
PERCH_LOGINPATH: (removed)
PERCH_PATH: (removed)
PERCH_CORE: (removed)
PERCH_RESFILEPATH: (removed)
Image manipulation: GD
PHP limits: Max upload 80M, Max POST 8M, Memory: 128M, Total max file upload: 8M
Resource folder writeable: Yes
HTTP_HOST: (removed)
DOCUMENT_ROOT: (removed)
REQUEST_URI:(removed)
SCRIPT_NAME:(removed)