I have just set up Tempo on our JIRA instance. The jira-administrators group has the team manager permission. I have added a user, which is also a member of jira-administrators, as team leader of the default team. However, when I click on get approval, the list of reviewers is empty. We're running JIRA 6.1 on Oracle and are using Crowd as user directory. On another JIRA instance, running on SQL Server and without crowd, I don't have this issue.