iCal sharing bug?

Hello everyone,

Here is my problem with iCal: One of my calendars is shared with a friend and also made public calendar. My friend mistakenly made some change on my calendar and I had to revert it. Anyway, it was only then that I found out the sharing control setting of iCal is not functioning as it should. I tried turning off his edit ability and also removed the check on Public Calendar but somehow it doesn't work, a few seconds after I did so everything was still the same, the calendar is still public calendar and my friend still have view & edit rights (I switched his right to View only but no use).

Does anyone have the same problem?

Btw, my system is iMac late 2012 with Mountain Lion 10.8.3; I have an iPhone 5 and an iPad 3 both of which using the same iCal.

Thank you.

Ch78