It should be upgrading the selected builds.
One thing that may not be explained clearly enough is how build selection works. When you click on one of the saved builds, it becomes highlighted, indicating that it is now the active build for that section. If no saved build is selected, the system defaults to using the “Previous Run” build for that section.
When you click the leftmost button out of the small buttons in the top right inside the build overview, all of your currently selected active builds should be displayed. These are the builds that the “Build ^” button is supposed to use when performing upgrades.
If that’s not what’s happening, then there may be an issue which i need to look into.