DAX: Puzzling ALL behaviour in context transition

[AlB]

Hi there,

I have the following calculated columns in the 'Product' table of the Contoso data model (available here). 'Product'[ProductKey] has 2517 unique values.

A) ‘Product’[Test 1]=CALCULATE(ALL(’Product’[ProductKey])) yields the ProductKey per row.

B) ‘Product’[Test 2]=CALCULATE(COUNTROWS(ALL(’Product’[ProductKey]))) however yields 2517 in all rows (size of the 'Product' table)

I find it puzzling that the filter resulting from context transition does affect the result in ‘Product’[Test 1] but it doesn't in ‘Product’[Test 2]. Could someone explain what is going on?

Thanks very much