Calendar Updates Not Updating On Invitees Calendar

I created an event directly from the iPhone calendar and invited a user. The invitee received the email with the attached ics file and it added the event to their calendar without any problems.

I then changed the date of the event and it sent another email with updated ics file. When they open the ics file this time it just displays the original event date and does not update their calendar to the new event date.

Below are the two ics files that were sent directly from iPhone calendar without any alterations. You should be able to recreate the problem by clicking on the "Original Invitation ics File" link to add the event to your calendar, then click on the "Update Invitation ics File" link which should update the previously added event but it does not.

Original Invitation ics File: https://dl.dropboxusercontent.com/u/15835767/original%20event.ics

Update Invitation ics File: https://dl.dropboxusercontent.com/u/15835767/updated%20event.ics