JIRA Calendar only displays Issue Key if more than one Issue Date is selected

Steps to Reproduce

1. Set up JIRA and Confluence with Team Calendars, and link the two systems
2. Create issues and versions in JIRA, with due dates, and resolved dates
3. Add a calendar using either Project, Saved Filter or JQL (not relevant to this scenario)
4. Select Issue Due Date only to display
   • Observe that the Issue Summary displays, but no Issue Key is displays
5. Edit the properties of the Calendar and select Issue Created Date to display as well
   • Observe that now, both Issue Created and Issue Due entries have the Issue Key displayed
6. Edit the calendar and select any combination of 2 or more of the 3 Issue Dates
   • Observe that issue keys are displayed
7. Edit the calendar and select only one of the Issue Dates
   • Observe that issue keys are not displayed
8. Edit the calendar and select only one of the Issue Dates along with the Version Due Date
   • Observe that issue keys are not displayed