With regards to your _2 statement about having to include all the columns. This is correct. By design, Aggr() ignores the chart dimensions. It is correct that you must list all dimensions to be used by aggr().
The difference is becasue the Product Category selection in the expression Vmedian_1 is respected
your expression is "Median(aggr(sum(x),employeeid))" so this will disregard the Dimension Product Category which
you have taken in the chart But if you select that dimension in the list box this Expression will be calculated
for that selection also . this is the reason for change in the result