SKPaymentQueue restoreCompletedTransactions restores the same transaction several times

I have a 6 month auto-renewable subscription set up in my purchases through iTunes connect. I created a test user and bought this subscription, now when I try to restore my purchases, it returns the same transaction several times in the transaction array in

- (void)paymentQueue:(SKPaymentQueue *)queue updatedTransactions:(NSArray *)transactions 

I am using the following code snippet to restore my purchases.

[[SKPaymentQueue defaultQueue] addTransactionObserver:self];
[[SKPaymentQueue defaultQueue] restoreCompletedTransactions];

Please let me know what I am doing wrong.

Thank.