Percentage Bar Chart does not work when using =monthname

[#1]

Hi everyone,

I am making a stacked bar chart and trying to show percentages.

the function is as follows:

Sum(sessions1)/Sum(TOTAL <browse_date> sessions1).

When using the date dimension everything is fine, because each day is measured as 100% (image 1.1), however once i change to =monthname(date) the chart changes into 100% for the total data (image 1.2).

Can someone point out what i might have done wrong?