Hi Crispin,

I confirm this as a bug. I just fixed it in my copy so it will be fixed in the next release. You can solve it immediately by running this sql script:

ALTER PROCEDURE [dbo].[mp_ForumSubscriptions_Unsub]

/*
Author:                Joe Audette
Created:            2013-08-17
Last Modified:        2013-11-22

*/

@SubGuid uniqueidentifier,
@CurrentUtc datetime

AS

UPDATE        [dbo].mp_ForumSubscriptions

SET            UnSubscribeDate = COALESCE(@CurrentUtc, getutcdate())

WHERE        SubGuid = @SubGuid        

GO

Thanks,

Joe