FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b99)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b99, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP
Professional
Version 2002
Service Pack 2

A DESCRIPTION OF THE PROBLEM :

If you run the code below you will get a table, scroll right to the last table select column 39 and start moving it to the left. The column will jump straight to the beginning of the table instead of a normal move. The move triggers scrollRectToVisible which outputs:
scroll to: left=0 right=75 visible: left=2511.0 right=3000.0
scroll to: left=0 right=75 visible: left=0.0 right=489.0
scroll to: left=0 right=75 visible: left=0.0 right=489.0
scroll to: left=0 right=75 visible: left=0.0 right=489.0

I think this bug is caused in BasicTableHeaderUI.mouseDragged(MouseEvent e)
....
//Cache the selected column.
int selectedIndex = table.convertColumnIndexToModel(getSelectedColumnIndex());

//Now do the move.
cm.moveColumn(columnIndex, newColumnIndex);

//Update the selected index.
selectColumn(table.convertColumnIndexToView(selectedIndex));
return;
...

selectedIndex is 0 and will be 0 after setting the new selected column. I think the call should be selectColumn(newColumnIndex), although the caching of the selectedIndex is probably done for a reason?

Testcase:
-- TestCase.java
import java.awt.*;
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
public class TestCase extends JFrame {
    public TestCase() {
        super("test");
        setPreferredSize(new Dimension(500, 500));
        createContent();
    }
    public void createContent() {
     setLayout(new BorderLayout());
        JTable table = new JTable() {
                @Override
                public void scrollRectToVisible(Rectangle aRect) {
                    double leftVisible = getVisibleRect().getX();
                    double rightVisible = getVisibleRect().getX() + getVisibleRect().getWidth();
                    System.out.println("scroll to: left=" + aRect.x
                                       + " right=" + (aRect.x + aRect.width)
                                       + " visible: left=" + leftVisible
                                       + " right=" + rightVisible);
                    super.scrollRectToVisible(aRect);
    }
            };
        table.setModel(new MyTableModel());
     table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
        JScrollPane sp = new JScrollPane(table);
     this.add(BorderLayout.CENTER, sp);
    }
    public class MyTableModel extends DefaultTableModel {
        @Override
        public int getColumnCount() {
            return 40;
        }
        @Override
        public String getColumnName(int column) {
            return "column " + column;
        }
        @Override
        public int getRowCount() {
            return 10;
}
@Override
        public Object getValueAt(int row, int column) {
            return "" + row + ", " + column;
}
    }
    /** @param args */
    public static void main(String[] args) {
        TestCase tc = new TestCase();
tc.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        tc.pack();
        tc.setVisible(true);
    }
}
--
STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
see above

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No "jumping" when scrolling
ACTUAL -
see above

REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
None, I can't override relevant methods

Release Regression From : 5.0u6
The above release value was the last known release where this
bug was not reproducible. Since then there has been a regression.