Strange indeed.
Actually this is a similiar problem that I mentioned
here .
The workaround is to set each event as a one-time repeating event so that it only repeats one time and on that day. Then it will display in the months past. Although this is not convenient, it does work.
Is there in the settings that is not right? I have it set so that Administrators can edit events and only Administrators can update Calendar.
EDIT: This
fix works on this problem.