This made it all very clear, thanks!
Sharing a project like this is very helpful for resource/library projects that multiple Teams can have access to.
I fell foul of this - and now I understand why. It would be great if there was a ‘shortcut’ icon
in the team that does not own the project, and/or another indicator of which team “owns” the project so that no one else tries to delete projects they think are duplicates of something that exists elsewhere. This is particularly likely to happen when duplicating the project because in the same screen you can move it to the new team, but end up retaining access to the new project within the original team. I couldn’t find a feedback to vote for related to this, so have created one here: Visual indicator to show that another team owns the project.