Issue Summary

Assignee, Reporter, and Watcher user picker fields do not find users when searching by email address.

Steps to Reproduce

1. Create a test user where email address is different than full name and username. Example:

   Full name	John Smith
   Username	jsmith
   Email address	ap86007@example.com

2. Open an existing issue and edit the Assignee, Reporter, or Watcher field.
3. Start typing the email. 
4. Do the same with a new issue. 

Expected Results

John Smith should be highlighted as a match. This used to be the case before 8.19.1. 

Actual Results

John Smith is not matched.

Workaround

Search using full name or username. 

Additional Information

This is inconsistent with other system user picker fields. Request Participant and Approver allow for searching by email.