This happens due to a rare networking issue. You have to rejoin the server to fix it, but basically the clientside prediction for brick deletion somehow disagreed with the serverside and now your client is certain the bricks aren't even there when in reality the deletion was rejected by the server and they are still there. This is usually characterized by weird, jerky collision behaviour that shows your player object is trying to fall through the "antibrick" on your side but is being updated to the previous position on the server side, as usually seen when ghosting new bricks while standing on something. You can actually get a similar bug where you ghost everything offset by a random vector; I think Port actually figured out how to cause that one.
It's hard for people like Badspot to actually deal with a bug like this because since the server has no idea anything's wrong with the client, it won't send the client ghosting packets to put the bricks back. And since the client thinks it knows for certain the bricks aren't there, it won't request any additional ghosting packets. This is probably a good thing for saving memory space on the server's side, since sending constant packets out to check the client isn't wrong about where absolutely everything is isn't exactly ideal.
If you rejoin, I can assure you the bricks will be back where they were.
And no, it's not new. It's been around for ages and me and some other people have studied it extensively.
(TL;DR Reconnect, it'll be fine)
