https://www.reddit.com/r/Minecraft/comments/ajed1j/minecraft_snapshot_19w04a_has_an_interesting_bug/

Also can be seen at 6:50 in this video:

https://youtu.be/zQYUPIxdz8w?t=416

I saw this port on Reddit about this and cold not find it here.

The user was able to walk along a floating and not change his elevation if you go right up against it. This also makes it hard to jump over any blocks.