Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* <code>{@link ReportDesignHandle#rename( DesignElementHandle )}</code>
	 * to change the element names.
	 * @param policy 
	 *  the policy for the clone action, maybe copy or copy for template
	 * @return Object the cloned design element.
	 * @throws CloneNotSupportedException
	 *             if clone is not supported.
	 */
	public Object doClone( CopyPolicy policy )
			throws CloneNotSupportedException
	{
		
		DesignElement element = (DesignElement) baseClone( );
		
		if ( policy != null )
			policy.execute( this, element );
		
		int slotCount = getDefn( ).getSlotCount( );
		if ( slotCount > 0 )
		{
			element.slots = new ContainerSlot[slotCount];
			for ( int i = 0; i < slotCount; i++ )
				element.slots[i] = slots[i].copy( element, i, policy );
		}
		return element;
	}
	/**
	 * Creates the slot with the definition.
	 */
	protected final void initSlots( )