Sorry if that title is a bit confusing. I'll try to explain it a bit better here than in the title. When you're trying to place a block at the side of another block, you hold shift (sneak), and you don't fall off of the block you're standing on, even though you're not actually completely on the block.
The bug I am reporting here is that in 20w27a, this also applies to flying in creative mode when the player is 0.6 or less blocks above a lower block and is using their sneak and jump keys at the same time.
I could not confirm this in 1.16.1, so this is likely related to the fix of
A player can fly above the block while sneak-jumping (I'm not really sure what to call that) without any restriction, but when trying to leave the area directly above that block (or any blocks next to it or next to those- same rules apply for sneaking in survival mode), they will not be able to.
- Place any block down.
- Fly 0.6 blocks or less above that block.
- Hold shift and space (or other keybinds for sneak and jump) at the same time.
- Notice how if you try to leave the area directly above that block, you will not be able to.
The video clip I am attaching (MojiraFlight2.mp4) shows the player in the nether. This bug can also be reproduced outside of the nether, that's just where I was when I recorded the clip. The video is only in 480p quality due to the file size limitations of Jira.
While working on my project (a massive piglin bartering farm with automatic sorting and shulker box filling), it was really difficult to have to un-sneak-jump-whatever-its-called every time I fly above a block. The machine has taken ten hours so far to make, and because everything in it is so close together, I experienced this bug a lot.