The Calendar plugin cannot consume iCal feeds from Jira

The confluence calendar plugin seems unable to display events from a Jira iCal feed.

To Reproduce

• Create a new calendar in confluence by clicking "add new calendar" on an instance of the calendar macro.
• Select "Subscription" in the location field
• Find a project calendar in jira and click on the "export in iCal Format" link
• insert this link into the url field in the new confluence calendar
• apply username/password as necessary to access the feed from confluence

Result

The calendar seems to subscribe normally to the jira iCal feed but none of the events appear on the calendar.
This result also occurs if instead of subscribing to the feed, you download it from jira and include it as an attachment and attempt to display it in the confluence calendar this way.

This bug is quite frustrating as I wish to subscribe to a number of jira projects' calendars in order to get an overview of the status of a number of projects on the one calendar.