How are projects included?

I’m not familiar enough with how this eclipse plugin works but how does it know what projects to included in the “OH2 Add-ons” working set?

I ask because I am having a weird thing occur. I switched back to a different branch (1225-russound) that includes the new russound binding - but the package didn’t appear in the working set. When I tried to import the project, it said the project was already part of the workspace (even though I couldn’t find it anywhere).

I’m wondering if my eclipse installation has become corrupted or if there is some file I didn’t commit?