See the discussion: http://mail.openjdk.java.net/pipermail/swing-dev/2016-April/005797.html

The text width can be differ for different graphics transforms.

To reproduce the issue run the following code sample on Windows:
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import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

public class CharWidthTest {

    static final String TEXT = "The quick brown fox jumps over the lazy dog"
            + "The quick brown fox jumps over the lazy dog";
    static final String LONG_TEXT = TEXT + TEXT.toUpperCase();

    public static void main(String[] args) {
        BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_RGB);

        Graphics2D g = img.createGraphics();
        int textWidth1 = g.getFontMetrics().stringWidth(LONG_TEXT);
        g.scale(2, 2);
        int textWidth2 = g.getFontMetrics().stringWidth(LONG_TEXT);
        g.dispose();

        if (textWidth1 != textWidth2) {
            throw new RuntimeException("Text size is different!");
        }
    }
}
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