Different results in MDX using aggregate function in SQL 2008 R2 and SQL 2012

I have a problem in SSAS where a strange behavior happen. I have a cube in prodution, but, for simulation, I created a small cube for isolate the problem. In this cube, there is one dimension and one fact. In [Sales Territory], I configured the UnknownMember property to true. In cube calculations, I put a simple scope code below:

SCOPE([Measures].[SalesAmountCustomValue]);
    THIS = [Measures].CurrentMember+10000000;
END SCOPE;

I execute the below MDX in SQL Server 2008 R2, and I have different results using and not using UnknownMember with Aggregate function. In SQL Server 2012, the result it's the same as expected.

WITH 
MEMBER [Sales Territory].[Sales Territory Country].[Countries] AS
  Aggregate(
      {
        [Sales Territory].[Sales Territory Country].[All].UNKNOWNMEMBER,
        [Sales Territory].[Sales Territory Country].&[9],
        [Sales Territory].[Sales Territory Country].&[6]
      }
  )
MEMBER [Measures].[SalesAmountCustomValueWithAggregate] AS
  (
    [Sales Territory].[Sales Territory Country].[Countries],
    [Measures].[SalesAmountCustomValue]
  ),
FORMAT_STRING="0,000;-0,000"
SELECT {
      [Measures].[SalesAmount],
      [Measures].[SalesAmountCustomValue],
      [Measures].[SalesAmountCustomValueWithAggregate]
   } ON 0
FROM AdventureWorks
WHERE {
    [Sales Territory].[Sales Territory Country].[All].UNKNOWNMEMBER,
    [Sales Territory].[Sales Territory Country].&[9],
    [Sales Territory].[Sales Territory Country].&[6]
  }

The result is:

SalesAmount: 11,038,845

SalesAmountCustomValue: 21,038,845

SalesAmountCustomValueWithAggregate: 41,038,845

Removing UnknownMember of aggregate function, the result is:

SalesAmount: 11,038,845

SalesAmountCustomValue: 21,038,845

SalesAmountCustomValueWithAggregate: 21,038,845

The behavior of MDX engine is different. In first exemple, the scope calculation is executed for each member before aggregate function. In this case, scope calculation is executed three times. The same occur putting a invalid member in aggregate function as [Sales Territory].[Sales Territory Country].&[AAA], but, in this case, scope calculation is executed two times in SQL 2008 R2 and SQL 2012.

Removing UnknownMember, scope calculation is executed one time, summing 10 billions.

I need to have the same behavior as in SQL 2012 for same MDX:

SalesAmount: 11,038,845

SalesAmountCustomValue: 21,038,845

SalesAmountCustomValueWithAggregate: 21,038,845

I tested the following versions:

SQL 2008R2 SP2 10.50.4279.0 x64

SQL 2012 11.0.2100.60 x64

Do you have any ideas about what is happening?

Thanks a lot in advance.

Paulo Corrêa