iPhone app has issues only if 3GS users upgrade in iTunes?

An upgrade to my app went live in iTunes. Only 3GS iPhones seem to be having an issue only if the 3GS did an upgrade of the app. If the 3GS iPhone does a fresh downlo开发者_JAVA技巧ad or deletes the app and then downloads it, everything is fine.

I'm wondering if I have missed something from a coding perspective that should have prevented this issue?

I used several 3GS iPhone testers. Those same 3GS iPhones that tested the adhoc fine, have the upgrade issue. iPhone 4s have no issues whether downloads are new or upgrades.

Is there a chance that the upgrade is not truly replacing the previous version of there app?

Is there an Xcode setting to ensure such a thing?

Or is this some kind of fluke?

I have upgraded other apps in the past with similar functionality and had no issues.

Did you had a breaking changes in your app data formats? If I remember correctly, iTunes upgrades backup the app data on the device and restores it back after the upgrade.