Applied the same logic as the fix for bug 894.

Anytime we enter the window, we gain the mouse focus.  If we leave the window because of a normal LeaveNotify, then we lose mouse focus.

src/video/x11/SDL_x11events.c

@@ -116,7 +116,9 @@ X11_DispatchEvent(_THIS)
             if (xevent.xcrossing.mode == NotifyUngrab)
                 printf("Mode: NotifyUngrab\n");
 #endif
-            if (xevent.xcrossing.detail != NotifyInferior) {
+            if (xevent.xcrossing.mode != NotifyGrab &&
+                xevent.xcrossing.mode != NotifyUngrab &&
+                xevent.xcrossing.detail != NotifyInferior) {
                 SDL_SetMouseFocus(NULL);
             }
         }