Flagged photos disappear from events

It seems sometimes when I flag photos within an event and post those flagged photos to facebook, via iphoto, the flagged photos *sometimes* get removed from the event and posted under "flagged photos" folder. Upon trying to copy them back into the event, I have no luck. Must I create an album of the event first, and copy from flagged to that? If this is the case, this is going to be VERY annoying. I had been wondering why I couldn't find the "good" pictures in some of my events, wondering where they all went. Having to make albums of all events is going to be time consuming.