FULL PRODUCT VERSION :
java version "1.5.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-b64)
Java HotSpot(TM) Client VM (build 1.5.0-b64, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
When a JPopupMenu is displayed as a heavyweight component (i.e. when it has no invoker or is displayed outside the bounds of its invoker) then the heavyweight component must have the window extended style WS_EX_TOOLWINDOW in order to act as a native popup menu under win32. This guarantees that the window does not get listed in ALT-TAB as the current implementation does.

REPRODUCIBILITY :
This bug can be reproduced always.