Category selection interface fails inside repeater

Hi

I am seeing the following issue with the Category selection interface inside a Collection.

I've replicated this in Safari 12.0.1 and FF 63.0.3

The process is as follows:

1. Add new repeater item
2. Choose a category from picker
3. Add another repeater
4. Category field is empty and does not load the Category selection interface

If I save the collection item and then add a new repeater it works again but the error follows the same pattern: First category field added fires up the Category selection UI and then silently fails if another one is added.

It also fails if I remove the group tags and change around the order of the fields in the template.

Edit template section is as follows:

<perch:group label="Certifications">
<perch:repeater id="product_certifications" label="Product certifications">
<perch:categories id="certification_category" label="Choose a Certification category" set="certifications" required>
<perch:content type="file" id="product_certification_link" bucket="downloads" label="Certification document">
</perch:repeater>
</perch:group>

Diagnostics:

Perch Runway: 3.1.3, PHP: 7.1.20, MySQL: mysqlnd 5.0.12-dev - 20150407 - $Id: 38fea24f2847fa7519001be390c98ae0acafe387 $, with PDO
Server OS: Darwin, apache2handler
Installed apps: content (3.1.3), assets (3.1.3), categories (3.1.3), jaygeorge_perch_admin_style (1), perch_forms (1.12)
App runtimes: <?php $apps_list = [ 'perch_forms', ];
PERCH_LOGINPATH: /perch
PERCH_PATH: /Users/ellimondo/Dropbox/Sites/accurate-safety/accurate-safety.com/perch
PERCH_CORE: /Users/ellimondo/Dropbox/Sites/accurate-safety/accurate-safety.com/perch/core
PERCH_RESFILEPATH: /Users/ellimondo/Dropbox/Sites/accurate-safety/accurate-safety.com/perch/resources
Image manipulation: GD
PHP limits: Max upload 32M, Max POST 32M, Memory: 128M, Total max file upload: 32M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
HTTP_HOST: dev.accurate-safety.local
DOCUMENT_ROOT: /Users/ellimondo/Dropbox/Sites/accurate-safety/accurate-safety.com
REQUEST_URI: /perch/core/settings/diagnostics/
SCRIPT_NAME: /perch/core/settings/diagnostics/index.php