Fix bug where changes to as previous instance would cause the current one to not be recognised as a change.
Fix bug where changes to as previous instance would cause the current one to not be
recognised as a change.

git-svn-id: 81e381228600e5752b80483efd2b45b26c451ea2@3160 e27351fd-9f3e-4f54-a53b-843176b1656c

trevor/calendarserver,trevor/calendarserver,trevor/calendarserver