FULL PRODUCT VERSION :
java version "1.6.0-rc"

A DESCRIPTION OF THE PROBLEM :
Swing uses Vectors where ArrayLists may be better candidates.  Vector methods are synchronized, ArrayLists are not.  Ive identified these candidate classes where Vector is mentioned and most likely used:
javax/swing/AbstractButton.java
javax/swing/ButtonGroup.java
javax/swing/CellRendererPane.java
javax/swing/DefaultComboBoxModel.java
javax/swing/DefaultListModel.java
javax/swing/JApplet.java
javax/swing/JComboBox.java
javax/swing/JComponent.java
javax/swing/JDesktopPane.java
javax/swing/JDialog.java
javax/swing/JEditorPane.java
javax/swing/JFileChooser.java
javax/swing/JFrame.java
javax/swing/JList.java
javax/swing/JMenu.java
javax/swing/JMenuBar.java
javax/swing/JOptionPane.java
javax/swing/JPopupMenu.java
javax/swing/JRootPane.java
javax/swing/JTabbedPane.java
javax/swing/JTable.java
javax/swing/JTree.java
javax/swing/JWindow.java
javax/swing/KeyboardManager.java
javax/swing/MenuSelectionManager.java
javax/swing/SwingUtilities.java
javax/swing/SystemEventQueueUtilities.java
javax/swing/UIDefaults.java
javax/swing/UIManager.java
javax/swing/#JTable.java#
javax/swing/event/TreeModelEvent.java
javax/swing/filechooser/FileSystemView.java
javax/swing/plaf/basic/BasicDesktopPaneUI.java
javax/swing/plaf/basic/BasicDirectoryModel.java
javax/swing/plaf/basic/BasicTabbedPaneUI.java
javax/swing/plaf/metal/MetalBumps.java
javax/swing/plaf/metal/MetalFileChooserUI.java
javax/swing/plaf/metal/MetalIconFactory.java
javax/swing/plaf/multi/MultiButtonUI.java
javax/swing/plaf/multi/MultiColorChooserUI.java
javax/swing/plaf/multi/MultiComboBoxUI.java
javax/swing/plaf/multi/MultiDesktopIconUI.java
javax/swing/plaf/multi/MultiDesktopPaneUI.java
javax/swing/plaf/multi/MultiFileChooserUI.java
javax/swing/plaf/multi/MultiInternalFrameUI.java
javax/swing/plaf/multi/MultiLabelUI.java
javax/swing/plaf/multi/MultiListUI.java
javax/swing/plaf/multi/MultiLookAndFeel.java
javax/swing/plaf/multi/MultiMenuBarUI.java
javax/swing/plaf/multi/MultiMenuItemUI.java
javax/swing/plaf/multi/MultiOptionPaneUI.java
javax/swing/plaf/multi/MultiPanelUI.java
javax/swing/plaf/multi/MultiPopupMenuUI.java
javax/swing/plaf/multi/MultiProgressBarUI.java
javax/swing/plaf/multi/MultiRootPaneUI.java
javax/swing/plaf/multi/MultiScrollBarUI.java
javax/swing/plaf/multi/MultiScrollPaneUI.java
javax/swing/plaf/multi/MultiSeparatorUI.java
javax/swing/plaf/multi/MultiSliderUI.java
javax/swing/plaf/multi/MultiSpinnerUI.java
javax/swing/plaf/multi/MultiSplitPaneUI.java
javax/swing/plaf/multi/MultiTabbedPaneUI.java
javax/swing/plaf/multi/MultiTableHeaderUI.java
javax/swing/plaf/multi/MultiTableUI.java
javax/swing/plaf/multi/MultiTextUI.java
javax/swing/plaf/multi/MultiToolBarUI.java
javax/swing/plaf/multi/MultiToolTipUI.java
javax/swing/plaf/multi/MultiTreeUI.java
javax/swing/plaf/multi/MultiViewportUI.java
javax/swing/plaf/synth/SynthDesktopPaneUI.java
javax/swing/plaf/synth/SynthTabbedPaneUI.java
javax/swing/table/DefaultTableColumnModel.java
javax/swing/table/DefaultTableModel.java
javax/swing/text/AbstractDocument.java
javax/swing/text/BoxView.java
javax/swing/text/CompositeView.java
javax/swing/text/DefaultHighlighter.java
javax/swing/text/DefaultStyledDocument.java
javax/swing/text/FlowView.java
javax/swing/text/GapContent.java
javax/swing/text/GapVector.java
javax/swing/text/JTextComponent.java
javax/swing/text/LayoutQueue.java
javax/swing/text/PlainDocument.java
javax/swing/text/PlainView.java
javax/swing/text/StringContent.java
javax/swing/text/StyleContext.java
javax/swing/text/TableView.java
javax/swing/text/WrappedPlainView.java
javax/swing/text/ZoneView.java
javax/swing/text/#AbstractDocument.java#
javax/swing/text/html/AccessibleHTML.java
javax/swing/text/html/CSS.java
javax/swing/text/html/HTMLDocument.java
javax/swing/text/html/HTMLWriter.java
javax/swing/text/html/Map.java
javax/swing/text/html/StyleSheet.java
javax/swing/text/html/TableView.java
javax/swing/text/html/parser/AttributeList.java
javax/swing/text/html/parser/ContentModel.java
javax/swing/text/html/parser/DTD.java
javax/swing/text/html/parser/Parser.java
javax/swing/text/html/parser/TagStack.java
javax/swing/text/rtf/RTFAttributes.java
javax/swing/text/rtf/RTFGenerator.java
javax/swing/text/rtf/RTFReader.java
javax/swing/tree/DefaultMutableTreeNode.java
javax/swing/tree/DefaultTreeCellEditor.java
javax/swing/tree/DefaultTreeModel.java
javax/swing/tree/DefaultTreeSelectionModel.java
javax/swing/tree/TreePath.java
javax/swing/tree/VariableHeightLayoutCache.java
javax/swing/undo/CompoundEdit.java
javax/swing/undo/StateEdit.java
javax/swing/undo/UndoManager.java
javax/swing/undo/UndoableEditSupport.java

these classes should be audited and replace Vectors, when possible, with ArrayLists

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
read swing source, look for Vector usage

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
ArrayLists being used everywhere.
ACTUAL -
116 classes that appear to be using Vectors.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
read java source, see Vector usage.
---------- END SOURCE ----------