Categories: Can't assign a category template (Perch Runway)

I'm unable to assign a category template to a category.

Under "Set Options" the category template shows up in the select dropdown normally. I select it, save changes, get the confirmation message ("Your set has been successfully edited. Return to category listing")

Yet it's not actually saved, the default "Category" template is still used.

Perch Runway: 2.8.2, PHP: 5.5.21, MySQL: 5.1.73, with PDO
Server OS: Linux, cgi-fcgi
Installed apps: content (2.8.2), assets (2.8.2), categories (2.8.2), perch_blog (4.6), collection_2 (2.8.2), collection_1 (2.8.2)
App runtimes: <?php $apps_list = array( 'content', 'categories', 'perch_blog', );
PERCH_LOGINPATH: /cms
PERCH_PATH: /nfs/mnt/1234/domains/xxx/html/cms
PERCH_CORE: /nfs/mnt/1234/domains/xxx/html/cms/core
PERCH_RESFILEPATH: /nfs/mnt/1234/domains/xxx/html/cms/resources
Image manipulation: GD
PHP limits: Max upload 62M, Max POST 64M, Memory: 128M, Total max file upload: 62M
Resource folder writeable: Yes
HTTP_HOST: xxx
DOCUMENT_ROOT: /home/1234/domains/xxx/html
REQUEST_URI: /cms/core/settings/diagnostics/
SCRIPT_NAME: /cms/core/settings/diagnostics/index.php

It doesn't matter which category template I choose, it's not saved.

Here is the category template I'd like to use:

<perch:category id="catDepth" type="hidden" /><figure id="client-<perch:category id="catSlug" type="slug" for="catTitle" />" class="item w1">
    <img src="<perch:category id="logo" type="image" bucket="clients" width="678" height="450" density="2" crop="true" label="Logo" order="2" required="true" />" alt="<perch:category id="catTitle" type="smarttext" label="Title" required="true" order="1" />" width="678" height="450" class="thumb" />
</figure><perch:category id="desc" type="textarea" label="Description" editor="markitup" markdown="true" size="s" suppress="true" />