DAX - KEEPFILTERS not showing correct results - arbitrarily shaped set

[snph1777]

I am doing some training work in AdventureWorksDW database.

I have two measures:   

Sum of SalesAmount = SUM(FactInternetSales[SalesAmount])

MonthlyAverageSales = AVERAGEX (
                                                            VALUES(DimDate[EnglishMonthName]),
                                                            [Sum of SalesAmount]
                                                          )

I have developed the above report, choosing only two years 2006 and 2007, and only 4 months using slicers.

While the measure [Sum of SalesAmount] shows the correct value, the other measure [MonthlyAverageSales] shows incorrect data in the Total row; however, both measures are right, when aggregated for each year 2006 and 2007.

The measure [MonthlyAverageSales] at the Total row should actually be $ 5,916,696.73/8, which is $ 739,587.09.  (8 in denominator represents 8 months - Jan,Feb,Nov,Dec for each year - 2006 and 2007)

Instead, what I see is $ 5,916,696.73/4, which is $1,479,174.18; (4 in denominator represents 4 months-  Jan,Feb,Nov,Dec, combining both years together)

Now, I have changed the formula, and have created a new measure:

MonthlyAverageCorrect = AVERAGEX (
                                                                KEEPFILTERS(VALUES(DimDate[EnglishMonthName])),
                                                                [Sum of SalesAmount]
                                                              )

I still do not see any change. Instead of getting $ 739,587.09, I still see $1,479,174.18.

Where am I in error ?