I suspect you mean that, when the app is installed via TestFlight and the app launches, it finds that the appStoreReceiptURL is nil. This is correct. An appStoreReceipt is only installed with an app when the app is installed from the production App Store. In all other cases, the installation of an app in the sandbox environment (which includes a production signed app via TestFlight) will not have an appStoreReceipt. After an in-app purchase, or after the iOS app makes the SKReceiptRefreshRequest call, then there will be an appStoreReceipt written to the app.
rich kubota - rkubota@apple.com
developer technical support CoreOS/Hardware/MFI