Why doesn't Netbeans debugger stop on runtime exceptions?

[Luigi Plinge]

If I enable Tools > Options > Miscellaneous > Java Debugger > Stop on uncaught exceptions, I would expect Netbeans to stop on an uncaught exception, but it doesn't.

e.g.

public class NewClass {
    public static void main(String[] args) {
        int a = 1/0;
    }
}

throws an ArithmeticException but the debugger does not stop. Or

public class NewClass {
    public static void main(String[] args) {
        int[] a = new int[5];
        a[6] = 1;
    }
}

throws an ArrayIndexOutOfBounds error, but again the debugger doesn't stop, so I can't see the variable values at the point of the exception.

Does anyone have any idea why this might be and how I can fix it?

I tried the same examples in Eclipse and the debugger there stopped as expected, so I might have to switch IDEs if I can't work this out.