Hi Hans, I believe that this is intended behavior - the filters within a WHERE clause of a metric are not transferred to a drill down.
You can see details about what filters are transferred
here in the documentation. Those are only these:
• Filters configured in the dashboard filter bar and active for the source insight.
• Filters configured in Analytical Designer for the target insight.
• Attribute value you click on in the source insight.
I am afraid that currently if you need some filter within a metric to work, it also needs to be part of the metric in the target insight.