JDK: 7b78+
Platforms: All

Method javax.swing.plaf.synth.SynthViewportUI.paintBorder(SynthContext context, Graphics g, int x, int y, int w, int h) inherits specification from javax.swing.plaf.synth.SynthUI which says:

"Paints the border."

http://download.java.net/jdk7/docs/api/javax/swing/plaf/synth/SynthViewportUI.html#paintBorder%28javax.swing.plaf.synth.SynthContext,%20java.awt.Graphics,%20int,%20int,%20int,%20int%29

In fact this method will not be called when JViewPort is shown on screen and this is actually mentioned in comments withing the method:

    /**
     * @inheritDoc
     */
    @Override
    public void paintBorder(SynthContext context, Graphics g, int x,
                            int y, int w, int h) {
        // This does nothing on purpose, JViewport doesn't allow a border
        // and therefor this will NEVER be called.
    }

Specification should be updated to tell explicitly that this method will not be called when viewport is repainted.