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
extends DialogPage
	implements IPreferencePage {
	/**
	 * Preference store, or <code>null</code>.
	 */
	private IPreferenceStore preferenceStore;
	/**
	 * Valid state for this page; <code>true</code> by default.
	 *
	 * @see #isValid
	 */
	private boolean isValid = true;
	/**
	 * Body of page.
	 */
	private Control body;
	/**
	 * Whether this page has the standard Apply and Defaults buttons; 
	 * <code>true</code> by default.
	 *
	 * @see #noDefaultAndApplyButton
	 */
	private boolean createDefaultAndApplyButton = true;
	/**
	 * Standard Defaults button, or <code>null</code> if none.
	 * This button has id <code>DEFAULTS_ID</code>.
	 */
	private Button defaultsButton = null;
	/**