When creating an event in the calendar that spans a few days, the final day of the event does not appear in the calendar. For example: an event that you set from the 1st of April to the 5th of April, the calendar only shows the 1st to the 4th marked with a dot. If you actively view the 5th an event is shown below but the absent dot is essential for an "at a glance" assessment of one's schedule.
Having installed IOS 6.1 I thought this issue might have been resolved, apparently not.
My father's iPhone 4S also has this issue so I'm fairly confident we're the only two people to have experienced this peculiar and irritating fault with the inbuilt calendar.