Clipping into a fence/wall using sneak and jump while placing a block in front
*This bug/glitch is also in 1.15.2, and might also be in earlier versions as well.
When I was building on a server, I clipped into a wall. This was a while ago, and I thought it was just a one time thing. Later I did testing, and it is an actual bug. I found it works in 1.15, and 1.16. The bug doesn't really affect things, as far as I know, but it could be showing some problems with the game that might have been normally unnoticed.
The bug is when there is two or more walls connected in a row. If you back into one at the short end, hold back, then jump and place a block you fall into one of the walls. I don't know why this happens, but it might be because of a bad computer, or maybe a hitbox thing? As in the hitbox doesn't change until you are inside of the wall?
As far as I know this works with any wall, and any full block that can attach to the wall.