Distinct Count Measure Group not distinct in MDX script

I am attempting run the following MDX query to determine the distinct amount of transaction numbers for a set including 2 dimension attributes. (POS and Concierge)  When I run the query, I seem to be getting the distinct amounts for each added to together.  If the same transaction number exists in both, they are both counted.  However if I attempt to get the same result using an Excel Pivot table, I get the desired transaction number count.  Could anyone help me with getting this result in the MDX query?

WITH

SET [Week]	AS StrToMember("[Date].[Hierarchy - Fiscal].[Fiscal Week].&[2012]&[48]")

SET [Store]	AS {[Financial Transaction Channel].[Transaction Channel Desc].&[POS],
			[Financial Transaction Channel].[Transaction Channel Desc].&[CONCIERGE]}


												
MEMBER [Store Transactions With Returns] AS
 	SUM([Week] * [Store], [Measures].[Operational Transactions Count])


SELECT
{
	[Store Transactions With Returns]
} ON COLUMNS,
{
	[Week]
} ON ROWS
FROM EDW
Results: 		Store Transactions With Returns
Wk. 48 - 2012 			78,636

The same attempt using an Excel Pivot table yields this:

If you add the POS and Concierge amounts, you get 78,636.  Which is the same result I am getting from my MDX query, but after I went through the transactions line by line, I was able to determine that 78,368 is the correct amount of distinct transaction numbers.

Any help on this would be greatly appreciated.