Division calculation is returning incorrect results

Hi All,

I have two measures: M1 and M2, and create new member:

CREATE MEMBER CURRENTCUBE.[Measures].[Average] AS 
    IIF(Not IsEmpty([Measures].[M2]) AND [Measures].[M2]=0,Null,[Measures].[M1]/[Measures].[M2])

And one Time Calculations:

CREATE MEMBER CURRENTCUBE.[Time].[Time Calculations].[TP] AS
SUM({[Time].[Time Calculations].DefaultMember} * { Members("[Time].[Date].[20120101]") : Members("[Time].[Date].["20120229]"))); 

The result is 

TP

M1M2 Average

What's wrong?

Thanks,

Andrew Huang