The Minecraft client moves even before the chunks from the server are fully loaded up. So the player will actually fall a bit (like 0.5/1 block?) before the client realizes that it was standing on a solid floor.
It would be better if the client would first wait for the chunks to receive and load up before it moves around on them.
This issue actually only show up if someone joins the server or teleports to unloaded chunk coordinates.
Linked issues
Comments
i can recall picking up so much falling momentum in a 1.3.2 server that i lost a full set of hearts when the chunk which i was supposed to be standing on finally loaded
Intended see MC-23.
Can be reproduced in singleplayer too. When chunk loading gets very slower, player can clip through empty air area where is actually unloaded chunks are.