The key rebinding mechanics of xmodmap stopped working when I updated from 3.2.0 to 3.3.0, and it seems GLFW has had issues with it. Now I see that this might have been fixed with GLFW 3.3.5, which also comes with a bunch of other bugfixes. But alas lwjgl comes with 3.3.4, even the nightly build.
I don't know if I can update glfw natives by myself, but I think it's beyond me, sine they're .jars.
I guess I'm asking kindly for a GLFW 3.3.5 wrap.