Demonstration
This bug is quite difficult to describe, and the size limit for uploading videos on this is not enough to show it well enough, so I put it on YouTube.
It would appear as though the root of the problem has to do with the velocity not being zeroed when colliding in a corner like in the video, which causes the camera bobbing setting to appear as though the player is moving in the block when they are not, and causes the strange direction at which the player flies when they jump.
How to reproduce
Turn on bobbing in video settings and walk into a corner pressing down two keys that do not make you unstuck from that corner. Let them go and press them again repeatedly to observe the camera movement. If bobbing isn't on the visual issue does not happen but the velocity will still be messed up when jumping up that block.
History
I loaded up like 50 different versions to try and find the exact version that this bug was introduced, and that version turned out to be 19w08b. Versions 19w08a and under do not have this bug. This is very odd because the only difference between the a and b version of 19w08 was a crash fix.
https://www.minecraft.net/en-us/article/minecraft-snapshot-19w08a
- duplicates
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MC-159952 Camera is shifting when trying to move against a block while in a corner when "Bobbing" is turned on
- Resolved