I'm experiencing the consequences of this problem and the issues discussed at
http://forums.omnigroup.com/showthread.php?t=22098
Feeling my way with setting up sync with my iCal calendars to indicate "off hours" I found that all-day events (such as family birthdays) are resulting in whole days being blocked off as unavailable. Despite having removed the subscription to the calendar concerned, all the exceptions remain in the resource calendar in OP with no obvious way to delete them. Worse still they are automatically inherited if you try to circumvent the problem by creating a new resource...
Help please! Currently my plans are unusable!