I have test html page whose size is 45K. I tried to read it with JEditorPane and I got the following. I attached the test.html.

To reproduce, simplely switch packages.html and test.html and run SwingSet demo.
and click HTML pane.

java.lang.StringIndexOutOfBoundsException: String index out of range: -21521
        at java.lang.String.<init>(String.java:150)
        at com.sun.java.swing.text.Segment.toString(Segment.java:79)
        at com.sun.java.swing.text.LabelView.sync(LabelView.java:367)
        at com.sun.java.swing.text.LabelView.getPreferredSpan(LabelView.java:112
)
        at com.sun.java.swing.text.BoxView.calculateAlignedSizeRequirements(BoxV
iew.java:609)
        at com.sun.java.swing.text.BoxView.checkRequests(BoxView.java:572)
        at com.sun.java.swing.text.BoxView.getPreferredSpan(BoxView.java:250)
        at com.sun.java.swing.text.ParagraphView.getPreferredSpan(ParagraphView.
java:103)
        at com.sun.java.swing.text.BoxView.calculateAlignedSizeRequirements(BoxV
iew.java:609)
        at com.sun.java.swing.text.BoxView.checkRequests(BoxView.java:572)
        at com.sun.java.swing.text.BoxView.getPreferredSpan(BoxView.java:250)
        at com.sun.java.swing.text.DefaultTextUI$RootView.getPreferredSpan(Defau
ltTextUI.java:700)
        at com.sun.java.swing.text.DefaultTextUI.getPreferredSize(DefaultTextUI.
java:469)
        at com.sun.java.swing.JComponent.getPreferredSize(JComponent.java:654)
        at com.sun.java.swing.ScrollPaneLayout.layoutContainer(ScrollPaneLayout.
java:502)
        at com.sun.java.swing.basic.BasicScrollPaneUI$BasicScrollPaneLayout.layo
utContainer(BasicScrollPaneUI.java:375)
        at java.awt.Container.layout(Container.java:462)
        at java.awt.Container.doLayout(Container.java:452)
        at java.awt.Container.validateTree(Container.java:523)
        at java.awt.Container.validateTree(Container.java:530)
        at java.awt.Container.validate(Container.java:505)
        at com.sun.java.swing.basic.BasicTabbedPaneUI.layoutContainer(BasicTabbe
dPaneUI.java:585)
        at java.awt.Container.layout(Container.java:462)
        at java.awt.Container.doLayout(Container.java:452)
        at com.sun.java.swing.basic.BasicTabbedPaneUI.stateChanged(BasicTabbedPa
neUI.java:624)
        at com.sun.java.swing.JTabbedPane.fireStateChanged(JTabbedPane.java:179)

        at com.sun.java.swing.JTabbedPane$ModelListener.stateChanged(JTabbedPane
.java:123)
        at com.sun.java.swing.DefaultSingleSelectionModel.fireStateChanged(Defau
ltSingleSelectionModel.java:96)
        at com.sun.java.swing.DefaultSingleSelectionModel.setSelectedIndex(Defau
ltSingleSelectionModel.java:50)
        at com.sun.java.swing.JTabbedPane.setSelectedIndex(JTabbedPane.java:219)

        at com.sun.java.swing.basic.BasicTabbedPaneUI$MouseGetter.mousePressed(B
asicTabbedPaneUI.java:915)
        at java.awt.AWTEventMulticaster.mousePressed(AWTEventMulticaster.java:21
9)
        at java.awt.Component.processMouseEvent(Component.java:2504)
        at java.awt.Component.processEvent(Component.java:2350)
        at java.awt.Container.processEvent(Container.java:889)
        at java.awt.Component.dispatchEventImpl(Component.java:1916)
        at java.awt.Container.dispatchEventImpl(Container.java:934)
        at java.awt.Component.dispatchEvent(Component.java:1826)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:1541
)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:1446)

        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:1382)
        at java.awt.Container.dispatchEventImpl(Container.java:921)
        at java.awt.Window.dispatchEventImpl(Window.java:517)
        at java.awt.Component.dispatchEvent(Component.java:1826)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:45)