The problem happens when using ui-beans which extend SUNs JPanel class.
They are used with a VB6 application and the ActiveX bridge.
Several references are hold by sun.beans.ole.JavaObjectInterface classes.
Some events are not released from the ActiveX bridge. A more detailed
analysis with screenshots of the memory profiler is provided with the
attached document "JPanel_Problem.doc".

To reconstruct the problem
When you extract the JPanelTest.zip file, you get two folders:
Beans and VB6. Before you can use the generate_beans_reg.bat in the
beans folder for creating the ./reg and ./tlb files, update the
variables USED_JRE_HOME and USED_BEANS_HOME in the batch file. After
generating the files, register the bean by double clicking the reg
file. The paneltest.jar also contains the java file for the bean.

The VB6 folder contains the VB6 project and the VB6 test application.
When you start JPanelTestApp.exe you will find a form with one button
(command 1). This button opens another form with the buttons "Add Java
Panel" and "Remove Java Panel". Using these buttons, a Swing Panel
should show up at the empty space of the form and disappear again. After
having added and removed several buttons, the memory leak can be seen
with a memory profiler (e.g. YourKit). Some screenshots for adding and
removing three times the JPanel is shown in document "JPanel_Problem.doc".

The faulty behaviour can be reproduced with JDK 1.3.1_11, JDK 1.3.1_12,
JDK 1.3.1_16.