I searched discussions about this topic but could not find any conclusive answer, so I prefer entering a new question.
The issue is the following. I have all my calendars on iCloud, and they sync to my iPhone.
I also have a private calendar on my Macbook that I do not want to move to iCloud. Using IOS 5 on my iPhone I was able to choose which calendars were synced automatically via iCloud and which ones were synced manually via iTunes. I had my private calendar set that way (i.e. it would sync via iTunes).
Now since I upgraded my iPhone to IOS 6, I no longer have this option: in iTunes, it says that "Your calendars are synced with your iPhone over the air".
Does this mean that "On My Mac" are now always private and never synced with any device (including via iTunes) ? Or is there some setting I missed that allows me to sync those via iTunes ?