Browse Users Permission Does Not Work For Customers in Service Desk Customer Portal

Summary

When adding a custom field (user picker) to the Customer Portal in Service Desk, customers are unable to use the user picker (even if they the Global Permission Browse Users)

Environment

Steps to Reproduce

1. Create a custom field that utilizes the user picker
2. Add custom field to a Service Desk Project Request Type
3. Ensure that Service Desk Customers are listed in Global Permissions Browse Users

Expected Results

User Picker works

Actual Results

User Picker does not appear. Field is a plain text field

Notes

Even adding Anyone to the Global Permission Browse Users does not work.
In previous version of JIRA, this used to work
ex: JIRA 7.1 & Service Desk 3.1.1

Workaround

Changing permission of users that can share as follows allows for customers to browse users in the customer portal: