Block placement while pillaring up can push you off the block.

If you pillar up with blocks your hitbox collides with the block and sends you off the block

so if you are building a house and keep pillaring up it might put you inside the block and you fall and if its high up you need to pillar all the way back up to keep building, which is extremely annoying

im not sure if its just on multiplayer but this is how you can recreate it (you might need to be in multiplayer)

you need to pillar up with blocks until it just shoves you off the edge of your block.

its a really bad bug because if you are high up it could push you off and if you dont have anything to save yourself you will die, and if your far away your stuff could despawn.