Problem with java when changing directory

Get this on some but not all directories where I keep Matlab m files:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Comparison method violates its general contract!
  at java.util.TimSort.mergeHi(Unknown Source)
  at java.util.TimSort.mergeAt(Unknown Source)
  at java.util.TimSort.mergeCollapse(Unknown Source)
  at java.util.TimSort.sort(Unknown Source)
  at java.util.TimSort.sort(Unknown Source)
  at java.util.Arrays.sort(Unknown Source)
  at java.util.Collections.sort(Unknown Source)
  at com.mathworks.widgets.grouptable.GroupingTableUtils.sortNonRecursively(GroupingTableUtils.java:296)
  at com.mathworks.widgets.grouptable.RowListTransactionTarget.finishTransaction(RowListTransactionTarget.java:115)
  at com.mathworks.widgets.grouptable.GroupingTableTransaction$1.run(GroupingTableTransaction.java:112)
  at java.awt.event.InvocationEvent.dispatch(Unknown Source)
  at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
  at java.awt.EventQueue.access$200(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.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)