Fixed modifier key events being lost.

README.md

@@ -73,6 +73,8 @@ The following dependencies are needed by the examples and test programs:
  - [Cocoa] Bugfix: One copy of each display name string was leaked
  - [Cocoa] Bugfix: Monitor enumeration caused a segfault if no `NSScreen` was
                    found for a given `CGDisplay`
+ - [Cocoa] Bugfix: Modifier key events were lost if the corresponding modifier
+                   bit field was unchanged
  - [Win32] Enabled generation of pkg-config file for MinGW
  - [Win32] Bugfix: Failure to load winmm or its functions was not reported to
                    the error callback

src/cocoa_window.m

@@ -617,18 +617,25 @@ static int translateKey(unsigned int key)
 - (void)flagsChanged:(NSEvent *)event
 {
     int action;
-    unsigned int newModifierFlags =
+    const unsigned int modifierFlags =
         [event modifierFlags] & NSDeviceIndependentModifierFlagsMask;
+    const int key = translateKey([event keyCode]);
+    const int mods = translateFlags(modifierFlags);
 
-    if (newModifierFlags > window->ns.modifierFlags)
+    if (modifierFlags == window->ns.modifierFlags)
+    {
+        if (window->key[key] == GLFW_PRESS)
+            action = GLFW_RELEASE;
+        else
+            action = GLFW_PRESS;
+    }
+    else if (modifierFlags > window->ns.modifierFlags)
         action = GLFW_PRESS;
     else
         action = GLFW_RELEASE;
 
-    window->ns.modifierFlags = newModifierFlags;
+    window->ns.modifierFlags = modifierFlags;
 
-    const int key = translateKey([event keyCode]);
-    const int mods = translateFlags([event modifierFlags]);
     _glfwInputKey(window, key, [event keyCode], action, mods);
 }