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/PDFBlockStackingLM.java
public int getHeight()
		{
			return this.height;
		}
		
		public boolean isEmpty()
		{
			return cache.isEmpty( );
		}
		
		public Iterator getChildren()
		{
			return cache.iterator( );
		}
		
		public IArea getFirst()
		{
			if(!cache.isEmpty( ))
			{
				return (IArea)cache.getFirst( );
			}
			return null;
		}
		
		public IArea removeFirst()
		{
			if(!cache.isEmpty( ))
			{
				AbstractArea area = ((AbstractArea)cache.removeFirst( )); 
				height -= area.getAllocatedHeight( );