Error on copy operation in STG

[Stan]

to produce the problem:
- create an STG
- create a transition, a place, and another transition
- connect them sequentially
- copy model to get an exception:

Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: Cannot select a node that is not in the current editing level (org.workcraft.dom.visual.connections.VisualConnection@136fa8e5), parent (null)
 at org.workcraft.dom.visual.AbstractVisualModel.validateSelection(AbstractVisualModel.java:205)
 at org.workcraft.dom.visual.AbstractVisualModel.validateSelection(AbstractVisualModel.java:213)
 at org.workcraft.dom.visual.AbstractVisualModel.addToSelection(AbstractVisualModel.java:258)
 at org.workcraft.Framework.loadVisualModelState(Framework.java:611)
 at org.workcraft.Framework.load(Framework.java:639)
 at org.workcraft.Framework.load(Framework.java:659)
 at org.workcraft.workspace.WorkspaceEntry.cancelMemento(WorkspaceEntry.java:212)
 at org.workcraft.workspace.WorkspaceEntry.copy(WorkspaceEntry.java:327)
 at org.workcraft.gui.MainWindow.copy(MainWindow.java:1172)
 at org.workcraft.gui.MainWindowActions$15.run(MainWindowActions.java:154)
 at org.workcraft.gui.MainWindow$1.actionPerformed(MainWindow.java:108)
 at org.workcraft.gui.actions.ActionMenuItem.fireActionPerformed(ActionMenuItem.java:58)
 at org.workcraft.gui.actions.ActionMenuItem.access$0(ActionMenuItem.java:55)
 at org.workcraft.gui.actions.ActionMenuItem$ActionForwarder.actionPerformed(ActionMenuItem.java:34)
 at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
 at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
 at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
 at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
 at javax.swing.AbstractButton.doClick(Unknown Source)
 at javax.swing.AbstractButton.doClick(Unknown Source)
 at javax.swing.plaf.basic.BasicMenuItemUI$Actions.actionPerformed(Unknown Source)
 at javax.swing.SwingUtilities.notifyAction(Unknown Source)
 at javax.swing.JComponent.processKeyBinding(Unknown Source)
 at javax.swing.JMenuBar.processBindingForKeyStrokeRecursive(Unknown Source)
 at javax.swing.JMenuBar.processBindingForKeyStrokeRecursive(Unknown Source)
 at javax.swing.JMenuBar.processBindingForKeyStrokeRecursive(Unknown Source)
 at javax.swing.JMenuBar.processKeyBinding(Unknown Source)
 at javax.swing.KeyboardManager.fireBinding(Unknown Source)
 at javax.swing.KeyboardManager.fireKeyboardAction(Unknown Source)
 at javax.swing.JComponent.processKeyBindingsForAllComponents(Unknown Source)
 at javax.swing.JComponent.processKeyBindings(Unknown Source)
 at javax.swing.JComponent.processKeyEvent(Unknown Source)
 at java.awt.Component.processEvent(Unknown Source)
 at java.awt.Container.processEvent(Unknown Source)
 at java.awt.Component.dispatchEventImpl(Unknown Source)
 at java.awt.Container.dispatchEventImpl(Unknown Source)
 at java.awt.Component.dispatchEvent(Unknown Source)
 at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
 at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
 at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
 at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
 at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
 at java.awt.Component.dispatchEventImpl(Unknown Source)
 at java.awt.Container.dispatchEventImpl(Unknown Source)
 at java.awt.Window.dispatchEventImpl(Unknown Source)
 at java.awt.Component.dispatchEvent(Unknown Source)
 at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
 at java.awt.EventQueue.access$000(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.awt.EventQueue$3.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at java.awt.EventQueue$4.run(Unknown Source)
 at java.awt.EventQueue$4.run(Unknown Source)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
 at java.awt.EventQueue.dispatchEvent(Unknown Source)
 at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.run(Unknown Source)