all member property

Month Dimension:

All Month
--Jan
--Feb
.
.
.
--Dec

All memeber property for month dimesion configure as mdx below :
max(descendants([DimMonth_HeadCnt].currentmember,[Mth]),[Measures].[No Head])

Problems :
The result show as below and it works fine at the pivot (excel).
All Month $1000
Jan $100
Feb $200
Mac $100
Apr $900
May $100
Jun $200
Jul $1000
Aug $200
Sep $300
Oct $300
Nov $200
Dec $300

But if user go to the pivot and select the filtering criteria to uncheck the Jul criteria, then result for 'All Month' still show $1000 instead of $900 as below:

All Month $1000
Jan $100
Feb $200
Mac $900
Apr $100
May $100
Jun $200
Aug $200
Sep $300
Oct $300
Nov $200
Dec $300


Any idea to solve this issue?
Thanks.