You can reproduce this bug by calling:

  FocusManager.setCurrentManager(FocusManager.getCurrentManager());
  
This will install an instance of DelegatingDefaultFocusManager as the
current KeyboardFocusManager. This FM delegates all of its functionality to
a wrapped KFM. However, because a KFM needs to be installed as the current
KFM in order to call the protected functions which query the global focus
state, the AWT starts throwing SecurityExceptions for all common focus
operations. Here's is one possible exception trace:

java.lang.SecurityException: this KeyboardFocusManager is not installed
in the current thread's context
        at
java.awt.KeyboardFocusManager.getGlobalFocusedWindow(KeyboardFocusMan
ager.java:622)
        at
java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFoc
usManager.java:457)
        at
javax.swing.DelegatingDefaultFocusManager.dispatchEvent(FocusManager.
java:235)
        at java.awt.Component.dispatchEventImpl(Component.java:3383)
        at java.awt.Container.dispatchEventImpl(Container.java:1440)
        at java.awt.Window.dispatchEventImpl(Window.java:1531)
        at java.awt.Component.dispatchEvent(Component.java:3353)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:439)
        at java.awt.SequencedEvent.dispatch(SequencedEvent.java:96)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:437)
        at
java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:15
0)
        at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:136)
        at
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:131)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:99)