Bug 178519 Problems in multi-rows header
Please see the attachments.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/layout/pdf/PDFTableLM.java
int tableWidth;
			if(specifiedWidth>0)
			{
				tableWidth = specifiedWidth;
			}
			else
			{
				tableWidth = maxWidth;
			}
			formalize(columns, tableWidth);
			return resolve(tableWidth, columns);
		}
		
		public int[] resolve( int specifiedWidth, int maxWidth )
		{
			assert ( specifiedWidth <= maxWidth );
			int columnNumber = table.getColumnCount( );
			int[] columns = new int[columnNumber];
			int columnWithWidth = 0;
			int colSum = 0;
			for ( int j = 0; j < table.getColumnCount( ); j++ )
			{
				IColumn column = (IColumn) table.getColumn( j );
				int columnWidth = getDimensionValue( column.getWidth( ),
						tableWidth );
				if ( columnWidth > 0 )
				{
					columns[j] = columnWidth;
					colSum += columnWidth;
					columnWithWidth++;