Bug 168026 Still use the existing data binding even though the aggregate is different
I had a table in which a data binding which aggregates on a group. When I insert a new data item in the report, although the expressions are same, it aggregates on All, then it refered to the existing data binding. The expected behavior would be a new data binding is created with different aggregates.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/ReportItemHandle.java
* expression that returns a string that is to appear in the Table of
	 * Contents for this item or its container.
	 * 
	 * @param expression
	 *            the expression that returns a string
	 * @throws SemanticException
	 *             if the TOC property is locked by the property mask.
	 * 
	 * @see #getTocExpression()
	 * @deprecated
	 */
	public void setTocExpression( String expression ) throws SemanticException
	{
		if ( StringUtil.isEmpty( expression ) )
		{
			setProperty( IReportItemModel.TOC_PROP, null );
			return;
		}
		TOCHandle tocHandle = getTOC( );
		if ( StringUtil.isBlank( expression ) )
			return;
		if ( tocHandle == null )
		{
			TOC toc = StructureFactory.createTOC( expression );
			addTOC( toc );
		}
		else
		{
			tocHandle.setExpression( expression );
		}