GLFW key input on GNOME 3 desktop - x11

Question

I've a problem with GLFW3 on a GNOME 3 desktop.
I've tested this on several Linux machines, including a fresh installed Ubuntu 16.04 LTS machine (with Unity).
The problem occurs in every GLFW3 application.
If i press and hold any key, a normal key GLFW_PRESS, and while holding the GLFW_REPEAT events are emitted.
But if I release the key, one GLFW_RELEASE event is emitted, following by another GLFW_PRESS (and sometimes multiple GLFW_REPEAT) events.
Here a minimal example:
#include <GLFW/glfw3.h>
#include <cstdio>
void glfw_key_callback(GLFWwindow* w, int key, int scancode, int action, int mods) {
printf("win %p: key %d, scancode %d, action %d, mods %d\n", w, key, scancode, action, mods);
}
int main() {
if (!glfwInit()) {
printf("Failed to init glfw!\n");
return 1;
}
GLFWwindow* window = glfwCreateWindow(800, 600, "Key input test", 0, 0);
glfwMakeContextCurrent(window);
glfwSetKeyCallback(window, glfw_key_callback);
while (!glfwWindowShouldClose(window)) {
glfwWaitEvents();
glfwSwapBuffers(window);
}
return 0;
}
Example output when I press and hold Space and release it after a few seconds:
win 0x104fb20: key 32, scancode 65, action 1, mods 0
win 0x104fb20: key 32, scancode 65, action 2, mods 0
...
win 0x104fb20: key 32, scancode 65, action 2, mods 0
win 0x104fb20: key 32, scancode 65, action 0, mods 0
win 0x104fb20: key 32, scancode 65, action 1, mods 0
win 0x104fb20: key 32, scancode 65, action 2, mods 0
win 0x104fb20: key 32, scancode 65, action 0, mods 0
I also have tried to compile and run this program with the current GLFW3 dev version (from https://github.com/glfw/glfw.git ) but with the same result.
Then i searched in the glfw3 source code where this events came from.
I found the XPending() call in the glfw3 source x11_window.c.
But it looks as that this additions events are emitted from the X11 system,
so I am not sure if this is a GLFW or X11 problem?
On other desktop environments such as Mate Desktop everything works fine for me.