ADDITIONAL SYSTEM INFORMATION :
java -version:
openjdk version "16.0.1" 2021-04-20
OpenJDK Runtime Environment (build 16.0.1+9-24)
OpenJDK 64-Bit Server VM (build 16.0.1+9-24, mixed mode, sharing)

Windows:
Windows 10 Pro for Workstations 20H2
19042.1052


A DESCRIPTION OF THE PROBLEM :
When a JPopupMenu is displayed as a reaction to a user interaction in a modal dialog, the user can not interact with any components inside the JPopupMenu - It seems to be blocked because of the Dialog being modal. This is independent from allwing/disabling lightweight popups

The same works flawlessly in Linux (Ubuntu 20.04)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run the attached class, click on the action and try to click any button in the resulting JPopupMenu:


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
It should be possible to interact with components in a JPopupMenu opened inside a modal Dialog
ACTUAL -
It is not possible to interact with components in the JPopupMenu opened inside a modal Dialog

---------- BEGIN SOURCE ----------
import java.awt.*;
import java.awt.event.ActionEvent;

public class PopUpAction extends javax.swing.AbstractAction implements
java.awt.event.WindowFocusListener
,java.awt.event.ActionListener
{
private static final int POPUPOFFSET=5;
private javax.swing.JToolBar toolbar=new javax.swing.JToolBar();
private javax.swing.JPopupMenu pmenu;
private java.util.List<javax.swing.Action> actions;

public PopUpAction()
{
super();
init();
}
public PopUpAction(java.lang.String name)
{
super(name);
init();
}
public PopUpAction(java.lang.String name, javax.swing.Icon icon)
{
super(name,icon);
init();
}
private void init()
{
actions=new java.util.LinkedList();
pmenu=new javax.swing.JPopupMenu();
pmenu.setLightWeightPopupEnabled(false);
}
public javax.swing.AbstractButton add(javax.swing.Action action)
{
actions.add(action);
javax.swing.AbstractButton btn=null;
if(action.getValue(javax.swing.Action.SELECTED_KEY)!=null)
{
javax.swing.JToggleButton jtb=new javax.swing.JToggleButton(action);
if(action.getValue(javax.swing.Action.SELECTED_KEY)!=null)
{
jtb.setSelectedIcon((javax.swing.Icon)action.getValue("SELECTED_ICON"));
}
btn=jtb;
toolbar.add(jtb);
}
else
btn=toolbar.add(action);
pmenu.add(btn);
btn.addActionListener(this);
return btn;
}
public void setOrientation(int o)
{
if(pmenu!=null)
pmenu.setVisible(false);
toolbar.setOrientation(o);
}
public void windowGainedFocus(java.awt.event.WindowEvent e)
{
}
public void windowLostFocus(java.awt.event.WindowEvent e)
{
if(pmenu!=null)
pmenu.setVisible(false);
}
public void actionPerformed(java.awt.event.ActionEvent evt)
{
java.lang.Object source=evt.getSource();
if(pmenu.isVisible()==true)
pmenu.setVisible(false);
else
{
try{
java.awt.Component c=(java.awt.Component)evt.getSource();
if(toolbar.getOrientation()==javax.swing.SwingConstants.VERTICAL)
{
pmenu.setLocation((int)(c.getLocationOnScreen().getX())+POPUPOFFSET,(int)(c.getLocationOnScreen().getY()+c.getHeight())-POPUPOFFSET);//,dialog.getWidth(),dialog.getHeight());
}
else
{
pmenu.setLocation((int)(c.getLocationOnScreen().getX()+c.getWidth())-POPUPOFFSET,(int)(c.getLocationOnScreen().getY())+POPUPOFFSET);//,dialog.getWidth(),dialog.getHeight());
}
pmenu.setVisible(true);
pmenu.requestFocusInWindow();
}
catch(java.awt.IllegalComponentStateException exp){}
}
}
public void clear()
{
actions.clear();
toolbar.removeAll();
}

public boolean isPopupVisible()
{
return pmenu.isVisible();
}

public static void main(java.lang.String[] args)
{
java.awt.Dialog dialog=new javax.swing.JDialog((java.awt.Frame)null,"title",true);
javax.swing.JPanel p=new javax.swing.JPanel(new java.awt.BorderLayout());
javax.swing.JToolBar tb=new javax.swing.JToolBar();
tb.setFloatable(false);
p.add(tb, BorderLayout.NORTH);
PopUpAction popUpAction=new PopUpAction("tata");
popUpAction.add(new javax.swing.AbstractAction("huhu")
{
@Override
public void actionPerformed(ActionEvent e)
{

}
});
popUpAction.add(new javax.swing.AbstractAction("hallo")
{
@Override
public void actionPerformed(ActionEvent e)
{

}
});

tb.add(popUpAction);
dialog.add(p);
dialog.pack();
dialog.setVisible(true);
}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
There is none known

FREQUENCY : always