Bug in visual calculations??

[FrankWe]

Hello,

actually I am working on a Pareto Table using visual calculations. I only use two columns from my data model ("Product" and "Sales Volume") and the rest of the columns I try to build as visual calculations in the visual directly to optimize performance. 

The calculations are working fine as long as I have less then 500 rows in the visual. When I have 500 or more rows in the visual the calculations of the values "Grand Totel" and "Cumulative Value %" are getting weired.  Here are the two calculations that I used to calculate the values:

Cumulative Value =
SUMX(

    WINDOW(

        0, ABS,

        0, REL, ROWS,

        ORDERBY([Pareto Value], DESC)),

        [Pareto Value]

)

Cumul Value % =

VAR calculatedValue = DIVIDE([Cumulative Value], COLLAPSEALL([Pareto Value], ROWS))

RETURN FORMAT(calculatedValue, "percent") )

Grand Total =
FORMAT(DIVIDE([Pareto Value], COLLAPSEALL([Pareto Value], ROWS)), "percent")

The result is looking like that. Including row 499 everything is fine but starting with row 500 the calculations are no longer correct. For me it looks like there is a bug with having more than 500 rows in a visual and the calculation of % values. As you can see in the screenshot the value in field "Cumulative Value" is correct for all rows. 

Is this really a bug or a limitation of "Visual Calculations"?