Analysis :: Excel 2013 Pivot-table / Grouping On Date That Comes From Analysis Service 2008?

I am using

SSAS: version 2008
Excel: version 2013

I am connecting to SSAS cube from Excel and I have date dimension with 4 fields (I have others but I don't use it for this case). I created 4 fields in order to test all possible scenarios that I could think of:

DateKey:
    - Type: System.Integer
    - Value: yyyyMMdd
Date:
    - Type: System.DateTime
DateStr0:
    - Type: System.String
    - Value: dd/MM/yyyy (note: I am not using US culture)
    - Example: 01/11/2015  
DateStr1:
    - Type: System.String
    - Value: %d/%M/yyyy (note: I am not using US culture) 
    - Example: 1/11/2015  

Filtering on date is working fine:

Initially, in excel, filtering on date was not working. But after changing dimensional type to time, and setting  DataType to Date, as mentioned in [URL] filter is working fine as you can see in the picture.Grouping on date is not working:

I have hierarchy in my Date dimension and I can group based on hierarchy, no problem. But user is used to pre-build grouping function of excel, and he wants to use that. Pre-build functions of Excel, Group and ungroup seems to be available as you can see in following picture:

But when user clicks 'Group', excel groups it as if it is a string, and that is the problem. User wants to group using pre-build grouping function available in Pivot table. I also find out that Power Pivot Table does not support this excel grouping functionality. And if I understood well, this pre-build grouping functionality of excel, needs to do calculation at run time, and that is not viable solution if you have millions of rows. So Power pivot table does not support pre-build grouping functionality of excel and hence we need to use dimension hierarchy to do the grouping. But I am not using Power Pivot table, I am using simple Pivot Table. So I expect grouping functionality to be working fine. Then I tried to do simple test. I created a simple data source in excel itself. And use it as source of my Pivot table. Then grouping is working fine. The only difference that I can see is (When double click the Measure value in Excel),For date values of my simple test, excel consider them as 'Date'.

For date values of my data coming from cube, excel consider them as 'General'

    2.1. But value here is same as it was in simple test.

    2.2. 'Date Filter' works just fine.

    2.3. If I just select this cell and unselect it, then excel change type to 'Date' though for that cell. 

    2.4. I have created 4 different types of fields in my date dimension thinking that values of attribute of my dimension might be the problem, but excel consider 'General' for all of them.

    2.5 This value (that can be seen when double clicking on measure) comes from 'Name Column' of the attribute. And the DataType defined is WChar. And I thought that might be the reason of issue. And I changed it to 'Date'. But SSAS does not allow it to change to 'Date' giving error : The 'Date' data type is not allowed for the 'NameColumn' property; 'WChar' should be used.

So, I don't know, what is the puzzle piece that I am missing.

1. Date filter works, group does not work

2. Excel consider it as 'General' string.

3. SSAS does not allow to change 'NameColumn' to Date.