Synopsis
The player can move faster than normal if you move diagonally by pressing two movement keys. It won't work if merely rotating your camera and pressing W.
The bug is most noticable when crouching, crawling or any other situation where the player is moving slowly. When crouching, pressing WD or WA results in aproximately 40% movement increase compared to only pressing W. The bug is still present when walking, sprinting, creative flying etc. however the speed increase from that is less than 5%.
To reproduce
Enter a world and time how long it takes to cover a set distance while crouching.
Ensure that you are only pressing one movement key during this time.
Then, time how long it takes while pressing two movement keys and moving diagonally.
Observed Results
Moving diagonally by while crouching gives you a 40% speed boost
Expected Results
This would not happen
Linked issues
relates to
Comments

For those interested here's a feedback post if you wish to discuss this. As the bug tracker is not the right place.
(If you can't log in look at pinned comment in WEB-6665 )

Update: there's a new feedback post for discussing and complains now. (Already 1.6k+ votes)
Link:
Petition to Revert Movement Changes MC-271065 and MC-241951 – Minecraft Feedback]

Bug fix has been reverted. See 25w04a's announcement article.

Requesting ownership. This bug has several issues (incorrect summary & description) I would like to correct them
Also the owner has been inactive for almost a year
Please post any feedback on the feedback website or feedback discord server, and have discussions on reddit or discord. The bug tracker comments section is not the place for feedback and discussions. Thanks!