FULL PRODUCT VERSION :
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+106-2016-02-17-181354.javare.4476.nc)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+106-2016-02-17-181354.javare.4476.nc, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Mac OS X 10.11.3 (15.3.0 Darwin Kernel Version 15.3.0: Thu Dec 10 18:40:58 PST 2015; root:xnu-3248.30.4~1/RELEASE_X86_64 x86_64)

A DESCRIPTION OF THE PROBLEM :
Merely calling JEditorPane.setText() with Devanagari text causes an ArrayIndexOutOfBounds exception on Java 9. See code sample.

While investigating incorrect rendering of Devanagari ligatures on OS X (https://sourceforge.net/p/omegat/bugs/800/), I came across JDK-7162125 and thought to try Java 9. I don't know for sure that the latter is related.

The issue does not occur in Java 8 or earlier.

REGRESSION. Last worked in version 8u73

ADDITIONAL REGRESSION INFORMATION:
java version "1.8.0_73"
Java(TM) SE Runtime Environment (build 1.8.0_73-b02)
Java HotSpot(TM) 64-Bit Server VM (build 25.73-b02, mixed mode)


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run supplied test case

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception
ACTUAL -
ArrayIndexOutOfBoundsException

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 40
at sun.font.ExtendedTextSourceLabel.createCharinfo(ExtendedTextSourceLabel.java:814)
at sun.font.ExtendedTextSourceLabel.getCharinfo(ExtendedTextSourceLabel.java:548)
at sun.font.ExtendedTextSourceLabel.getLineBreakIndex(ExtendedTextSourceLabel.java:480)
at java.awt.font.TextMeasurer.calcLineBreak(TextMeasurer.java:330)
at java.awt.font.TextMeasurer.getLineBreakIndex(TextMeasurer.java:566)
at java.awt.font.LineBreakMeasurer.nextOffset(LineBreakMeasurer.java:359)
at java.awt.font.LineBreakMeasurer.nextLayout(LineBreakMeasurer.java:440)
at javax.swing.text.TextLayoutStrategy.sync(TextLayoutStrategy.java:324)
at javax.swing.text.TextLayoutStrategy.insertUpdate(TextLayoutStrategy.java:70)
at javax.swing.text.FlowView.loadChildren(FlowView.java:151)
at javax.swing.text.CompositeView.setParent(CompositeView.java:139)
at javax.swing.text.FlowView.setParent(FlowView.java:297)
at javax.swing.text.CompositeView.replace(CompositeView.java:217)
at javax.swing.text.BoxView.replace(BoxView.java:182)
at javax.swing.text.CompositeView.loadChildren(CompositeView.java:114)
at javax.swing.text.CompositeView.setParent(CompositeView.java:139)
at javax.swing.plaf.basic.BasicTextUI$RootView.setView(BasicTextUI.java:1369)
at javax.swing.plaf.basic.BasicTextUI.setView(BasicTextUI.java:707)
at javax.swing.plaf.basic.BasicTextUI.modelChanged(BasicTextUI.java:696)
at javax.swing.plaf.basic.BasicTextUI$UpdateHandler.insertUpdate(BasicTextUI.java:1903)
at javax.swing.text.AbstractDocument.fireInsertUpdate(AbstractDocument.java:203)
at javax.swing.text.AbstractDocument.handleInsertString(AbstractDocument.java:754)
at javax.swing.text.AbstractDocument.insertString(AbstractDocument.java:713)
at javax.swing.text.PlainDocument.insertString(PlainDocument.java:131)
at javax.swing.text.DefaultEditorKit.read(DefaultEditorKit.java:274)
at javax.swing.JEditorPane.setText(JEditorPane.java:1423)
at DevanagariTest.main(DevanagariTest.java:5)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.JEditorPane;

public class DevanagariTest {
    public static void main(String[] args) {
        new JEditorPane().setText("\u0930\u093E\u0915\u094D\u0937\u0938");
    }
}

---------- END SOURCE ----------