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
*            The property definition. Must be valid. Can be a
	 *            system-defined or user-defined property.
	 * @param value
	 *            The value to set. Must be valid for the property.
	 */
	public void setProperty( ElementPropertyDefn prop, Object value )
	{
		assert prop != null;
		String propName = prop.getName( );
		
		
		if ( prop.isIntrinsic( ) )
		{
			setIntrinsicProperty( propName, value );
			return;
		}
		
		if ( prop.getTypeCode( ) == PropertyType.ELEMENT_REF_TYPE )
		{
			ElementRefValue oldRef = (ElementRefValue) propValues
					.get( propName );
			updateReference( oldRef, (ElementRefValue) value, prop );
		}
		
		if ( prop.getTypeCode( ) == PropertyType.STRUCT_REF_TYPE )
		{
			StructRefValue oldRef = (StructRefValue) propValues.get( propName );
			updateReference( oldRef, (StructRefValue) value, prop );
		}