Unsubscribe URLs in SNS http(s) notifications broken

Hello,

today I noticed that the UnsubscribeURLs in notifications sent to HTTP(S) endpoints no longer get populated correctly. It seems there is a problem with the string expansion. Here is an example:

"UnsubscribeURL":"https://sns.eu-west-1.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=CLOUDCAST_SUBSCRIPTION_GUID_PLACEHOLDER"

As you can see from the example, this occurred in eu-west-1 but I have not examined any other regions. Please look into this and fix, as our product has to rely on this information.

Regards, Christoph