Redactor links in Perch 3

Good morning,

We have an issue with a customer trying to add links to documents from within Redactor in a recently launched Perch 3 site. Unfortunately it seems as though the link text cannot be customised in any way. Is there a way we can get around this? I presumed highlighting the text we'd like to use as the link would work but that didn't help...

I made a quick video to show what's happening (and what the customer needs): https://www.dropbox.com/s/21t0teyhu9dloyr/naming-links.mov?dl=0

Perch: 3.0.12, PHP: 7.1.9, MySQL: 5.5.53-38.5, with PDO
Server OS: Linux, litespeed
Installed apps: content (3.0.12), assets (3.0.12), categories (3.0.12), root_analytics (2.0.0), perch_blog (5.6.1), perch_forms (1.9.1), redfinch_logger (1.0.1)
App runtimes: <?php $apps_list = [ 'perch_blog', 'perch_forms', 'root_analytics' ];
PERCH_LOGINPATH: /admin
PERCH_PATH: /home/root6/public_html/admin
PERCH_CORE: /home/root6/public_html/admin/core
PERCH_RESFILEPATH: /home/root6/public_html/admin/resources
Image manipulation: GD Imagick
PHP limits: Max upload 512M, Max POST 512M, Memory: 256M, Total max file upload: 256M
F1: 3b606135b33e6a102526838f4152a807
Resource folder writeable: Yes
HTTP_HOST: elmsfarmcottages.co.uk
DOCUMENT_ROOT: /home/root6/public_html
REQUEST_URI: /admin/core/settings/diagnostics/
SCRIPT_NAME: /admin/core/settings/diagnostics/index.php

Thanks in advance, Lea.