This issue is related to https://bugs.launchpad.net/karl3/+bug/880873
There is a duplication issue occurring with existing events in certain communities. See this Justice Initiative community for an example: https://karl.soros.org/communities/justice-initiative-administration/calendar/month.html?year=2011&month=10&day=18
You will see that events are repeated once in the This Calendar's Events only layer and an additional time in the other layer that the event should appear in. This problem is that we can't recreate this issue with newly created events in a test community. We need to take a look and try and figure out what is going on here before doing the work for LP# 880873. It may be that the new calendar code has not been applied retroactively to existing events. Let us know if there are any questions on this.
I have reason to believe that this is fixed now. See my screenshot that I made on branch1, after fixing the related bug.
So if this is still happening, it can be reopened. But then it should go to the next week iteration, because it will require more testing in this case.