Bug 41927 [Dialogs] Selecting in PreferenceDialog generates too many invalid entries
20030825 If you select an entry, close the dialog and then reopen it selecting anotehr entry will result in a "this page has invalid values" although you selected nothing.
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
* The container this preference page belongs to; <code>null</code>
	 * if none.
	 */
	private IPreferencePageContainer container = null;
	/**
	 * Standard Apply button, or <code>null</code> if none.
	 * This button has id <code>APPLY_ID</code>.
	 */
	private Button applyButton = null;
	/**
	 * Description label.
	 * 
	 * @see #createDescriptionLabel.
	 */
	private Label descriptionLabel;
	/**
	 * Caches size of page.
	 */
	private Point size = null;
	/**
	 * Creates a new preference page with an empty title and no image.
	 */
	protected PreferencePage() {
		this(""); 
	}
	/**
	 * Creates a new preference page with the given title and no image.
	 *
	 * @param title the title of this preference page
	 */