Broken federation of discussion post to Mastodon

I just made a discussion post to !Openstreetmap@feddit.uk, which is visible here: https://piefed.social/c/osm@feddit.uk/p/2091360/towards-an-open-federated-review-platform-based-on-osm

However, when federated to Mastodon, the post link is broken. It directs here, as if it was made to a local community: https://piefed.social/c/osm/p/2091360/towards-an-open-federated-review-platform-based-on-osm

This was pointed out by a user of sfba.social: https://sfba.social/@FinchHaven/116641561263747414