GroupBy aggregation method with parameter

Hi community, I need some help with GroupBy node aggregation methods which require a parameter, as the Quantile method does. I am experiencing unexpected results while setting the parameter to 0.25 (for the first quartile value, or any other, BTW) and getting back always the 0.5 quantile value. May the use of flow variables in the node affect its functioning? What am I missing there? I’ll much appreciate comments regarding this point.