Steps to reproduce:
1. Minimise the window using the amber "-" icon at the top of the window frame.
2. Focus another application.
3. Restore the window by clicking on the thumbnail image of it in the Dock (*not* clicking on the Application Icon).
4. Notice that the window no longer receives left mouse down events reliably (you have to hit it several times, sometimes double clicking).

Investigation:

If the user restores the application by clicking on the Application icon in the Dock, it works correctly. The problem only occurs when the restoring from the thumbnail image of the window in the Dock, and also only if another application was focused while the window was minimized. The difference between these two ways of restoring the application is that:
  - When clicking on the Application icon, the application is made active first, and then the window is made visible (raised).
  - When clicking on the Window thumbnail, the window is made visible first and the application becomes active later.

The problem seems centre around calling [nswindow makeKeyAndOrderFront:nil] in Cocoa_RaiseWindow ( http://hg.libsdl.org/SDL/file/a31313cfa891/src/video/cocoa/SDL_cocoawindow.m#l1234 ) when the application is not active. This happens because the 'visible' observer is the first thing that triggers when restoring the application from the thumbnail in the dock. The application activation message happens somewhat later.

I notice also that once makeKeyAndOrderFront has been called while the application is inactive, the window does not in fact become key, and furthermore, even once the application becomes active later, calls to makeKeyAndOrderFront fail to make the window key.

I have identified two possible fixes. 

1. If the application is not active in Cocoa_RaiseWindow, just call [nswindow orderFront:nil] instead of [nswindow makeKeyAndOrderFront:nil].

2. Return early from observerValueForKeyPath if the application is not active: if (![NSApp isActive]) return;






Related to #1996