Bug 200312 Chart Variables are still in the bottom right pane when select other categories [13]
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ExpressionBuilder.java
* Create an expression builder under the given parent shell with the given
	 * initial expression
	 * 
	 * @param parentShell
	 *            the parent shell
	 * @param initExpression
	 *            the initial expression
	 */
	public ExpressionBuilder( Shell parentShell, String initExpression )
	{
		super( parentShell );
		title = DIALOG_TITLE;
		this.expression = UIUtil.convertToGUIString( initExpression );
	}
	protected void setShellStyle( int newShellStyle )
	{
		newShellStyle |= SWT.MAX | SWT.RESIZE;
		super.setShellStyle( newShellStyle );
	}
	/**
	 * Create an expression builder under the default parent shell with the
	 * given initial expression
	 * 
	 * @param initExpression
	 *            the initial expression
	 */
	public ExpressionBuilder( String initExpression )
	{
		this( UIUtil.getDefaultShell( ), initExpression );
	}