Hi,
I've taken a look and it appears you may be right. When you change or save an occurence in a series, there is a field called IsChangedOccurence. This is set to false when the series is created. If an occurence is saved, then this is set to true. It appears that when this field is set to true, it no longer shows in the calendar. I'll submit this to the team and update this thread when I hear back.
- Adam