Close JIRA ticket from Gitlab

We are using gitlab-ce-8.4.4-ce.0.el6.x86_64 on one RHEL6 server and are connecting to a single JIRA instance containing many projects on another RHEL6 server. Each JIRA project uses a separate JIRA key, and we would like to close any JIRA issue with a merge. We are using the ‘standard’ git development process, with feature branches merging into develop, then develop into a release branch, and finally release into master. Comments do get added to JIRA tickets for pushes, commits, merge requests and merges using the rest/api/2 URL. But closing the JIRA ticket does not happen with a merge using the Fixes, Resolves or Closes keywords, the ‘Accepting this merge request will close issue XXX’ line does not appear in the ‘Accept merge request’ window, nor do I see anything in the production.log that tells me it even makes the attempt. All I see are the ‘JiraService SUCCESS’ messages for the rest api calls.

  1. Are the JIRA ‘close’ log messages in some other log?
  2. What JIRA URL is used to make the close status change?
  3. Why is it that some merges send email, and others do not?
  4. Are there any JIRA add-ons needed for the status change to occur?