We've had this problem on the international Galaxy S II for a while now. There is a thread on it here: http://forum.xda-developers.com/show....php?t=1192696
One problem I see is that the source is for the Android AOSP calendar, which is probably different from the Samsung calendar (just like the Email app is different). I haven't tried the AOSP calendar but typically the Samsung apps have more features. You would have to edit the smali files to fix the Samsung app (or do a crude replacement hack like my Exchange wakelock hack, and pray that it works).
In the meantime, my solution was to just uninstall Calendar. Works great, but now I have no calendar.
Other users have uninstalled Calendar and used replacement calendar apps without the wakelock issue, so you could try that.
I also noticed that one user mentioned that this bug only happens when Calendar notifications are set to "Off." Kinda counterintuitive, but try setting Calendar notifications to something other than "Off" and see if that fixes the problem.