I think I've answered the question:

http://webhelp.episerver.com/latest/cms-edit/project-user-interface.htm#Versioning

It says, in part:

• "It is only one version of a page that is associated with the project."
  
  

This would make the "reversion issue" correct, since you created a new Draft (a new version), then deleted it (by reverting), so that version no longer exists to be associated with the project.

Here's what confused me (from the link above):

• "You can only have one published version, so if you publish another version of the page (that is, a version that is not associated with the project) after the version associated with the project, the project version is not published anymore and therefore set as Previously published in the project overview."
  
  

I couldn't figure this out because it seemed that the page attachment "survived" multiple republishes. I would make another change, then republish, and it would stay attached to the project. Here's what I didn't realize --

I was still in the project when I made the change. So every time I did that, the new version was being added to the project, and the old version removed. So what appeared to be a page-centric project attachment, was really version-centric, and the version that was attached just swapped out invisibly to me (I never "saw" the swap happen, and just assumed that it was the same thing all along).

It might help to have a version number on the project overview page. I think this would make it more explicit that it's this version that's attached, not the page itself.