Recently a question was migrated from Earth Science to the main Sustainability.SE site, and it shows up on the main page:
Then, it was migrated to meta, as you can see here. Now, the link is on both the main site and meta. Both links take you to the same place.
Actually the question was not migrated from Earth Science but reposted here by the OP. I tried to find his question on Earth Science but I think the OP has deleted it there.
When I moved the question from the Sustainability main site to Meta I did expect it to be removed from the main site entirely and only show up in Meta, so I was a bit surprised at first that this is not the case. It could be that this functionality was changed recently, or perhaps my expectations were simply incorrect. It's rare that we move questions from main to meta, so I can't verify how it worked in the past. In any case I don't think there is a bug here.
