EDIT: This bug comes from GLFW. This issue has been fixed in newer versions, but Minecraft ships with an older version of GLFW where the bug has not been fixed.

Video demonstration of the bug: https://www.youtube.com/watch?v=8h5Jif6zyDs

In the video, there is a little overlay that shows which keys I press.

• If I press and hold 'W', I immediately start moving forward immediately.
• If I simultaneously press and hold 'W' and my spring key at the same time, I move forward but there is a small delay before I start moving forward.
• If I simultaneously press and hold 'W', my sprint key, and 'Spacebar' all at the same time, I do not move forward. Instead, I only jump in place.
• If I press and hold 'W', my sprint key, and 'Spacebar' but begin pressing them at different times, the bug does not trigger.

This bug triggers very often and is very disruptful to the gameplay. It can very easily get you killed.