User Doesn't Exist Error When Trying to Remove an External User From a Project Role

When a user is deleted from LDAP, if he/she has any individual project roles in JIRA, you cannot remove the user from the project roles. You will get the "User does not exist" error when you attempt to do so.

Steps to Reproduce

1. Create a LDAP User
2. Sync the LDAP User into JIRA
3. Add the LDAP user to a project role (Administrators, Developers or Users)
4. Remove the LDAP User from LDAP
5. Sync the LDAP Directory again in JIRA Administration >> Users >> User Directories
6. Try to remove the LDAP user from the project role (you will get the User Does not Exist Error)

Workaround

Simply restart JIRA, which will auto-remove the user from the project role