On Linux, simultaneously pressing two keys introduces a delay for one of the keys pressed

When pressing two or more keys on the same frame/tick, one of them will only be considered pressed after a delay specified by xset r rate. Pressing another key while this delay happens entirely drops the key to be pressed.

This breaks sprinting, walking diagonally, and jumping forward.

Workaround: set the XMODIFIERS environment variable to "@im=null", or "@im=xim".

Fix:
1) apply the patch from here to the 3.2.2 source tree, and compile it (thanks, comment-608172)
2) add -Dorg.lwjgl.librarypath="/path/to/library/" to the launcher options (write the folder it's in, not the .so file itself)

If you do not want to bother with recompiling glfw, I have a precompiled binary for arch linux at https://i.selic.re/libglfw.so
(If a mod can confirm there's no malicious edits, that would be nice!)