X11: Fix glfwSetWindowMonitor not flushing buffer

README.md

@@ -247,6 +247,7 @@ information on what to include when reporting a bug.
 - [X11] Bugfix: Update cursor position on enter event (#1366)
 - [X11] Bugfix: `glfwSetWindowMonitor` did not update hints when resizing
                 non-user-resizable windows
+- [X11] Bugfix: `glfwSetWindowMonitor` did not flush output buffer in some cases
 - [Linux] Added workaround for missing `SYN_DROPPED` in pre-2.6.39 kernel
           headers (#1196)
 - [Linux] Moved to evdev for joystick input (#906,#1005)

src/x11_window.c

@@ -2410,6 +2410,7 @@ void _glfwPlatformSetWindowMonitor(_GLFWwindow* window,
                               xpos, ypos, width, height);
         }
 
+        XFlush(_glfw.x11.display);
         return;
     }