class cast exception preventing Jalview Project restore

Jalview project load fails with usual 'failed to load jalview project', and stack trace like the following is generated:
java.lang.ClassCastException
at javax.swing.LayoutComparator.compare(LayoutComparator.java:61)
at java.util.Arrays.mergeSort(Arrays.java:1286)
at java.util.Arrays.mergeSort(Arrays.java:1281)
at java.util.Arrays.sort(Arrays.java:1210)
at java.util.Collections.sort(Collections.java:159)
at javax.swing.SortingFocusTraversalPolicy.enumerateAndSortCycle(SortingFocusTraversalPolicy.java:119)
at javax.swing.SortingFocusTraversalPolicy.getFirstComponent(SortingFocusTraversalPolicy.java:434)
at javax.swing.LayoutFocusTraversalPolicy.getFirstComponent(LayoutFocusTraversalPolicy.java:148)
at javax.swing.SortingFocusTraversalPolicy.getDefaultComponent(SortingFocusTraversalPolicy.java:511)
at javax.swing.InternalFrameFocusTraversalPolicy.getInitialComponent(InternalFrameFocusTraversalPolicy.java:49)
at javax.swing.JInternalFrame.getMostRecentFocusOwner(JInternalFrame.java:1415)
at javax.swing.JInternalFrame.restoreSubcomponentFocus(JInternalFrame.java:1444)
at javax.swing.JInternalFrame.setSelected(JInternalFrame.java:1096)
at jalview.gui.Desktop.addInternalFrame(Desktop.java:633)
at jalview.gui.Desktop.addInternalFrame(Desktop.java:485)
at jalview.gui.Jalview2XML.loadViewport(Jalview2XML.java:3229)
at jalview.gui.Jalview2XML.LoadFromObject(Jalview2XML.java:2446)
at jalview.gui.Jalview2XML.LoadJalviewAlign(Jalview2XML.java:1651)
at jalview.gui.Jalview2XML.LoadJalviewAlign(Jalview2XML.java:1549)
at jalview.gui.Desktop$12.run(Desktop.java:1245)
at java.lang.Thread.run(Thread.java:680)