J2SE Version (please include all output from java -version flag):
 java version "1.5.0_10"
 Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_10-b03)
 Java HotSpot(TM) Client VM (build 1.5.0_10-b03, mixed mode, sharing)

 java version "1.6.0_01-ea"
 Java(TM) SE Runtime Environment (build 1.6.0_01-ea-b01)
 Java HotSpot(TM) Client VM (build 1.6.0_01-ea-b01, mixed mode, sharing)

Does this problem occur on J2SE 1.3, 1.4.x or 1.5? Yes / No (pick one)
 Yes

Operating System Configuration Information (be specific):
 Win_xp

Bug Description:
  The minimized windows will disapear if the height of the window was reduced.

Attached you can find a sample to reproduce it.
Steps:

1. Execute the sample (see attached screenshot1)
2. minimize some or all of the frames (see attached screenshot2)
3. reduce the height of the Window (see attached screenshot3)