When I am walking through a small hallway or a door in a multiplayer server with a bit of lag, it will sometimes snap me back a few blocks because the server thought I walked into a wall or the side of a door, but the client showed me to continue walking. I will usually ignore it and keep walking until I notice that I can't interact with blocks like doors or chests. When I log out and back in, it will put me back where I hit the wall or door. This has happened less in 1.4.4, but it was not fixed.