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
* Adds a bound column to the list.
	 * 
	 * @param addColumn
	 *            the bound column to add
	 * @param inForce
	 *            <code>true</code> the column is added to the list regardless
	 *            of duplicate expression. <code>false</code> do not add the
	 *            column if the expression already exist
	 * @param column
	 *            the bound column
	 * @return the newly created <code>ComputedColumnHandle</code> or the
	 *         existed <code>ComputedColumnHandle</code> in the list
	 * @throws SemanticException
	 *             if expression is not duplicate but the name duplicates the
	 *             exsiting bound column. Or, if the both name/expression are
	 *             duplicate, but <code>inForce</code> is <code>true</code>.
	 */
	public ComputedColumnHandle addColumnBinding( ComputedColumn addColumn,
			boolean inForce ) throws SemanticException
	{
		if ( addColumn == null )
			return null;
		String expr = addColumn.getExpression( );
		if ( expr == null )
			return null;
		List columns = (List) getProperty( BOUND_DATA_COLUMNS_PROP );
		if ( columns == null )
			return (ComputedColumnHandle) getPropertyHandle(
					BOUND_DATA_COLUMNS_PROP ).addItem( addColumn );
		ComputedColumn column = DataBoundColumnUtil.getColumn( columns, expr );