To reproduce this bug, run the regression test at
  test/java/awt/event/HierarchyEvent/SpecTest/SpecTest.html.

The test produces a series of messages of the following form:
warning (known bug): changed for DISPLAYABILITY_CHANGED event incorrect
warning (known bug): changedParent for DISPLAYABILITY_CHANGED event incorrect
warning (known bug): changed for DISPLAYABILITY_CHANGED event incorrect
warning (known bug): changedParent for DISPLAYABILITY_CHANGED event incorrect
...

This bug occurs because DISPLAYABILITY_CHANGED HierarchyEvents are generated
inside Component.addNotify and Component.removeNotify, which are called from
several different places in the AWT, and could also be called from client code. There is currently no way to figure out whether a particular call to
addNotify or removeNotify is the first call in the recursion, or where the
first call (and hence the correct 'parent' field) was.