If I filter my "Do" section to only show Focused tasks, I feel the header should reflect how many tasks I have based on that filter. This way when looking at the header number, I don't see that I have 45 tasks but when I click on that section, I only have 3 focused tasks showing.
The "Review&Organize" section already shows me the total count of single actions if I wanted to see a birds eye view of everything. I feel the "Do" section is a filtered area of what's important to me and the number of tasks on the header should reflect my options for that section.
As an example, I only ever show "Focused" task in the "Do" section. I would never want to see how many single actions I have when looking at the header. It makes it useless for me.
Someone may prefer to always filter the "Do" section by upcoming or overdue tasks.
Just an idea is all.