Bug 236324 [Forms] Eclipse 3.4 crashes / failes to repaint when "Close Others" is used with SharedHeaderFormEditor
bundles/org.eclipse.ui.forms/src/org/eclipse/ui/internal/forms/widgets/FormImages.java
int length, boolean vertical, Color bg) {
		checkHashMaps();
		ImageIdentifier id = new ComplexImageIdentifier(display, colors, length, percents, vertical, bg);
		ImageReference result = (ImageReference) images.get(id);
		if (result != null && !result.getImage().isDisposed()) {
			result.incCount();
			return result.getImage();
		}
		Image image = createGradient(display, colors, percents, length, vertical, bg);
		images.put(id, new ImageReference(image));
		ids.put(image, id);
		return image;
	}
	
	public boolean markFinished(Image image) {
		checkHashMaps();
		ImageIdentifier id = (ImageIdentifier)ids.get(image);
		if (id != null) {
			ImageReference ref = (ImageReference) images.get(id);
			if (ref != null) {
				if (ref.decCount()) {
					images.remove(id);
					ids.remove(ref.getImage());
					ref.getImage().dispose();
					validateHashMaps();
				}
				return true;
			}
		}