Task example: produce/consume button doesn't work (known issue due to list variables)

Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: The notificationQueues might not be empty (false) so any shadow variables might be stale so score calculation is unreliable.
Maybe a ScoreDirector.before*() method was called without calling ScoreDirector.triggerVariableListeners(), before calling ScoreDirector.calculateScore().
	at org.optaplanner.core.impl.domain.variable.listener.support.VariableListenerSupport.assertNotificationQueuesAreEmpty(VariableListenerSupport.java:270)
	at org.optaplanner.core.impl.score.director.stream.DroolsConstraintStreamScoreDirector.calculateScore(DroolsConstraintStreamScoreDirector.java:85)
	at org.optaplanner.examples.common.business.SolutionBusiness.doProblemChange(SolutionBusiness.java:363)
	at org.optaplanner.examples.common.swingui.SolutionPanel.doProblemChange(SolutionPanel.java:208)
	at org.optaplanner.examples.common.swingui.SolutionPanel.doProblemChange(SolutionPanel.java:204)
	at org.optaplanner.examples.taskassigning.swingui.TaskAssigningPanel.produceUpTo(TaskAssigningPanel.java:165)
	at org.optaplanner.examples.taskassigning.swingui.TaskAssigningPanel.lambda$createHeaderPanel$2(TaskAssigningPanel.java:111)
	at java.desktop/javax.swing.Timer.fireActionPerformed(Timer.java:317)
	at java.desktop/javax.swing.Timer$DoPostEvent.run(Timer.java:249)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:313)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)