[MC-4352] Players occasionally float into the floor to be bounced back when the server realises.

Above is a video of the issue. It was made by GunfighterJ in the #bukkit IRC channel, but I've experienced this issue myself.

It happens sometimes on spawn. I connect to a server, I spawn on the ground, I start drifting into the floor. The problem is fixed by reconnecting.

Linked issues

I am the GunfighterJ referred to in this video. This happens to everyone that connects and it is a randomly occurring event.

Players are also unable to place/break blocks as the result of this.

This ticket is invalid as it relates to a modded or 3rd party client/server.

Any non-standard client/server build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the plugin creator.
This site is for addressing issues related to the base unmodded MineCraft.

It's definitely client-side. It has nothing to do with the server.