In some Agile boards, I get the old look (buttons at the top right for "Backlog", "Active Sprints" and "Reports").
In others, I get the new look (tabs on the left side for "Backlog", "Active Sprints", "Releases", "Reports", "Components", etc)
The only difference I can see offhand is that my board filters for the new look include issues from exactly one project, and board filters for the old look include issues from more than one project.
If I'm right, why does this difference exist?