--- old/src/java.desktop/macosx/classes/sun/lwawt/macosx/CPlatformWindow.java	2018-01-29 17:53:55.000000000 +0530
+++ new/src/java.desktop/macosx/classes/sun/lwawt/macosx/CPlatformWindow.java	2018-01-29 17:53:55.000000000 +0530
@@ -799,9 +799,12 @@
                 toggleFullScreen();
             }
 
-            final RootPaneContainer rpc = (RootPaneContainer) target;
-            rpc.getRootPane().putClientProperty(
+            Frame[] frame = Frame.getFrames();
+            if ((Frame)target == frame[0]) {
+                final RootPaneContainer rpc = (RootPaneContainer) target;
+                rpc.getRootPane().putClientProperty(
                     CPlatformWindow.WINDOW_FULLSCREENABLE, canFullScreen);
+            }
         }
     }