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
while ( iter.hasNext( ) )
						{
							AbstractArea child = (AbstractArea) iter.next( );
							child.setAllocatedPosition( child.getAllocatedX( ),
									child.getAllocatedY( ) + offset );
						}
					}
					else if ( IStyle.MIDDLE_VALUE.equals( verticalAlign ) )
					{
						Iterator iter = root.getChildren( );
						while ( iter.hasNext( ) )
						{
							AbstractArea child = (AbstractArea) iter.next( );
							child.setAllocatedPosition( child.getAllocatedX( ),
									child.getAllocatedY( ) + offset / 2 );
						}
					}
				}
				height = specifiedHeight;
			}
		}
		root.setHeight( height );
	}
	public boolean addArea( IArea area, boolean keepWithPrevious, boolean keepWithNext )
	{
		
		if ( area == null )
		{
			return true;
		}