While swimming up flowing water(using the new diving/swimming animation), and brushing up against a wall, the player is sometimes teleported into the wall, and takes suffocation damage. If you mine the block, you no longer take suffocation damage and are standing in a 1x1 block. I managed to reproduce this numerous times while exploring underwater caves.

After writing this, I went and replicated the bug again, this time I took pictures:

Here is the setup for the bug:

https://imgur.com/zFDO51m

All you have to do is press CTRL to swim, fight against the current, then press jump at the same time. You will be teleported into the ceiling, or a wall nearby. here are two pictures of being teleported into the ceiling:

https://imgur.com/rUXqrTZ

https://imgur.com/8Z3bL7G

This is very easy to replicate, assuming the setup is correct.