From analysis I have done.
Affects both local calendars and remote (as in iCal or Exchange)
By the next day all events will clear so the view is empty and a respring is then needed to bring the day back and show upcoming events
Respring only works to refresh and pick up new events incoming, or changes to events that happen in the day. (i.e. if an event is moved locally, or if a remote event is moved, removed or updated) 4.0.3.15 suffers from these issues on iOS5 running on iPhone 4
Have successfulyl checked & tested on another iPhone 4 with 4.0.3.13 installed and the calendar pluging does not have these problems. Updates, changes, new events etc work and refresh with no need to resring. Something broke between v.13 and v.15