RANKX does not give correct result when used in SUMMARIZECOLUMNS and SUMMARIZE

[marcussyliu]

In this DAX query, the returned values for Rank by Sales column look strange. If the filter context from Sales table is commented, the result is correct. The same issue was found with SUMMARIZE too. As the moment, I can work around by nesting the column name and columns expression in ADDCOLUMNS expression, but I wanted to understand what's going wrong internally with SUMMARIZE or SUMMARIZECOLUMNS in this case? Could anyone help? Thanks! 

EVALUATE
SUMMARIZECOLUMNS (
    'Product'[Brand],
    Sales,
    "Total Sales", [Total Sales],
    "Rank by Sales", RANKX ( ALL ( 'Product'[Brand] ), [Total Sales] )
)