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I only have MS Exchange synced OTA with my iPhone calendar and it happens to me all the time. I also checked with some colleagues phones and they all have the same issue with calendar app.

Not sure why it doesn't affect everyone, will make it a bit harder to debug.
 
I can reproduce this bug on an iPhone 3G running iOS 4.1. Only it happens every time I start the Calendar application, not just after a forced closing or reboot.
I'm using MobileMe, but after restoring the phone and setting up wired sync, I get the same behavior.

pretty annoying 😡 😱
 
Sorry for the late reply, but 4.2.1 release fixed this issue.

Wish it did. Just got a replacement iphone due to bad home button. After getting my google & hotmail setup via exchange I see the calendar list issue. Running 4.3.2
 
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