Can anyone spot the problem with my trigger?

[daveperry]

In SQL Server 2005, I have an update trigger on a table. The purpose of this trigger is to set or clear a DeactivatedDate field whenever the IsActive field is changed. Also to write an audit record keeping a record of the change. Here is an excerpt from the trigger:

DECLARE @prevIsActive BIT		
DECLARE @newIsActive BIT
DECLARE @id BIGINT

SELECT @newIsActive = IsActive, @id = RecordId
FROM inserted

IF UPDATE(IsActive)	
BEGIN	
	SELECT @prevIsActive = IsActive FROM deleted
	IF @newIsActive < @prevIsActive
	BEGIN	--deactivated
		UPDATE Customers 
		SET DeactivatedDate = GETDATE() 
		WHERE CustomerId=@id 
	END
	ELSE
	BEGIN	--activated
		UPDATE Customers 
		SET DeactivatedDate = NULL 
		WHERE CustomerId=@id 
	END

	--Add an entry to the audit table with OpType 6 indicating deactivated and OpType 7 indicating activated.
	INSERT INTO AuditCustomers (CustomerId, OpType, UserId)
	SELECT i.CustomerId, CASE i.IsActive WHEN 1 THEN 7 ELSE 6 END, i.UserId
	FROM Inserted AS i
	INNER JOIN Deleted AS d ON i.CustomerId = d.CustomerId
	WHERE i.IsActive <> d.IsActive
END

This trigger is working in 99% of cases. However, in the other 1% of cases, when a customer is deactivated, the audit record is created correctly with OpType=6, proving that the trigger must have fired, but the DeactivatedDate remains null. How is this possible, can anybody tell me?