Dax Calculate Function

I have been wrestling to understand how logically the following to statements or (measures) are providing different results. 

Sales PCT_1 =

    var current_sales = sumx(sales, Sales[Quantity]*Sales[Net Price])

    var all_sales = calculate(current_sales,all('Product Category'[Category]))

    var pct_ratio = DIVIDE(current_sales,all_sales,0)

    return pct_ratio

Sales PCT_2 =

    var current_sales = sumx(sales, Sales[Quantity]*Sales[Net Price])

    var all_sales = calculate(sumx(sales, Sales[Quantity]*Sales[Net Price]),all('Product Category'[Category]))

    var pct_ratio = DIVIDE(current_sales,all_sales,0)

    return pct_ratio

(the first one provides all results 100% and ingnores all filters even while the later one provides better results when I categorise the result)

I would be gratefull if someone help me how using the statement or the variable have made the changes.

Thanks in advance.