On multiplayer servers ever since 1.9+ the client has allowed you to fall into blocks you have just placed.

An example can be seen from these gifs here
1.8 client - https://gyazo.com/51282f95131683d063d9eb96015cf770

As you can see from that gif there are no issues when looking at your feet, holding down jump and placing blocks underneath you.

1.9+ client - https://gyazo.com/148ceb46660a6064a31a297450e64f48
the client constantly falls into the blocks you just place, bumping you off of your tower making it incredibly hard to tower up.

Reproduced the issue using the official 1.9 Minecraft server, can only seem to reproduce it with a latency. When testing I had 250ms latency (Australia --> USA), when testing with no latency or localhost cant reproduce.

Prior to 1.9 this issue was never present (I believe the jumping height changed in 1.9, possibly to do with this?).

The client is receiving a teleport packet when it teleports the player and messes them up.

Sequence of packets - http://i.imgur.com/G8SS7Xc.png
The server doesn't change the block until after it teleports you out which is weird.