Restricting articles by label on JSM Customer portal is not returning any results

Issue Summary

This is reproducible on Data Center: (yes)

Steps to Reproduce

1. Link a JSM project to a Confluence DC instance with a Confluence version 8.6.0 or greater
2. Restrict the search for a specific request type to a label in Confluence - See https://confluence.atlassian.com/servicemanagementserver/write-and-search-for-knowledge-base-articles-956713329.html 
3. Create an article with that label in Confluence
4. In JSM, On that request type in Customer portal, type the article title into the Summary

Expected Results

The article should show in the search results

Actual Results

No articles are returned

Workaround

Change the label restriction in JSM to "global:[label]"