When drawing a large version of ♫ (\u266B) with g.drawString() the font changes: the connecting beam points down, instead of up and the glyph is suddenly smaller. FontMetrics still reflect the width and height of what a properly scaled glyph would have looked like. This last fact makes this especially problematic, as the glyphs cannot be positioned properly anymore.

Demo Code:
==========

import javax.swing.*;
import java.awt.*;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;

public class UnicodeFontMetricsIssues {

    public static void main(final String[] args) {
        final String note = "\u266B";
        final String xNoteY = "\u266BY";
        final String xY = "XY";

        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(new BorderLayout());
        final JPanel iconPanel = new JPanel(new FlowLayout());
        frame.getContentPane().add(iconPanel, BorderLayout.CENTER);
        final TextIcon noteIcon = new TextIcon(note);
        final TextIcon xNoteYIcon = new TextIcon(xNoteY);
        final TextIcon xYIcon = new TextIcon(xY);
        iconPanel.add(noteIcon);
        iconPanel.add(xNoteYIcon);
        iconPanel.add(xYIcon);
        final JSlider slider = new JSlider(1, 2000, 1);
        slider.setSnapToTicks(false);
        final JPanel sliderPanel = new JPanel(new FlowLayout());
        sliderPanel.add(slider);
        final JLabel scaleFactorLabel = new JLabel("1.0");
        sliderPanel.add(scaleFactorLabel);
        frame.getContentPane().add(sliderPanel, BorderLayout.SOUTH);

        slider.addChangeListener(e -> {
            final float scaleFactor = slider.getValue()/100f;
            noteIcon.setScaleFactor(scaleFactor);
            xNoteYIcon.setScaleFactor(scaleFactor);
            xYIcon.setScaleFactor(scaleFactor);
            scaleFactorLabel.setText("" + scaleFactor);
            frame.invalidate();
        });

        SwingUtilities.invokeLater(() -> {
            frame.setSize(500, 800);
            frame.setVisible(true);
        });
    }

    private static class TextIcon extends JLabel {

        private final String text;

        public TextIcon(final String text) {
            this.text = text;
            setIcon(createIconWithText(1f));
        }

        public void setScaleFactor(final float scaleFactor) {
            setIcon(createIconWithText(scaleFactor));
        }

        private ImageIcon createIconWithText(final float scaleFactor) {
            final int width = 400;
            final int height = 200;
            final BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
            final Graphics2D g2d = (Graphics2D)image.getGraphics();

            g2d.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);

            final float originalSize = g2d.getFont().getSize2D();
            g2d.setFont(g2d.getFont().deriveFont(originalSize * scaleFactor));

            final FontMetrics metrics = g2d.getFontMetrics();

            // fill whole background
            g2d.setColor(Color.GREEN);
            g2d.fillRect(0, 0, width, height);

            // draw string bounds as RED background
            final Rectangle2D rect = metrics.getStringBounds(text, g2d);
            g2d.setColor(Color.RED);
            g2d.fillRect((width - (int) rect.getWidth()) / 2, 0, (int)rect.getWidth(), (int)rect.getHeight());

            // draw string
            g2d.setColor(Color.BLACK);
            g2d.drawString(text, (width - (int) rect.getWidth()) / 2, metrics.getAscent());
            g2d.dispose();
            return new ImageIcon(image);
        }
    }
}


The demo code lets you change the size of the font, showing a scale factor. The RED background shows the bounding box for the string.

The issue is illustrated in the attached screenshots and movie.