When QCS is merging published mailbox into the existing one, is existing Calendars content merged as well or overwritten?
When merging users QCS assumes that published object contains the master copy of all the information - this includes AD attributes as well as Calendar and Free/Busy. As such QCS overwrites the Calendar upon the first publish and every subsequent republish event. In between only delta calendar changes are getting synchronized. Please keep this QCS behavior in mind when performing user merges.