To reproduce this bug, first launch the AWT Conformance test using the latest
promotion of JDK 1.1.7 (currently K). The 1.1 version of this test can be found
at /net/oakum.eng/export/disk0/green1/SCCS_DIRECTORIES/JDK-brutus.AWT/test/java/
awt/CONFORMANCE.
  
From the "Test" menu, select "Persistent serialization --> Save serialized
state...". Specify a filename, click OK, and then exit the test.

Now, load in the 1.2 version of the AWT Conformance test using the FCS H build.
This version of the test can be found at
  <1.2 ws>/test/java/awt/CONFORMANCE.

From the "Test" menu, select "Persistent serialization --> Load serialized
state...". Specify the same filename and click OK.
The following exception appears:

java.io.InvalidClassException: [Ljava.awt.Component;; Serializable is incompatible with Externalizable
        at java.io.ObjectStreamClass.validateLocalClass(ObjectStreamClass.java:458)
        at java.io.ObjectStreamClass.setClass(ObjectStreamClass.java:482)
        at java.io.ObjectInputStream.inputClassDescriptor(ObjectInputStream.java:776)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:348)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:227)
        at java.io.ObjectInputStream.inputArray(ObjectInputStream.java:793)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:352)
        at java.io.ObjectInputStream.inputClassFields(ObjectInputStream.java:1822)
        at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:497)
        at java.awt.Container.readObject(Container.java:1497)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.io.ObjectInputStream.invokeObjectReader(ObjectInputStream.java:1676)
        at java.io.ObjectInputStream.inputObject(ObjectInputStream.java:1156)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:364)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:227)
        at AWTConformanceTest.loadSerializedFile(AWTConformanceTest.java:424)
        at AWTConformanceTest.loadSerialize(AWTConformanceTest.java:439)
        at AWTConformanceTest.actionPerformed(AWTConformanceTest.java:371)
        at AWTConformanceTest.actionPerformed(AWTConformanceTest.java:337)
        at java.awt.MenuItem.processActionEvent(MenuItem.java:453)
        at java.awt.MenuItem.processEvent(MenuItem.java:417)
        at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:236)
        at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:226)
        at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:238)
        at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:226)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:260)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:68)
Serialization error -- please file a bug report

The Exception does not appear when running with the "G" build. Note that
Component and Container are both declared Serializable, but not Externalizable,
in 1.1 and 1.2.