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
* 
	 * <p>
	 * When inserting the cloned element into the design tree, user needs to
	 * care about the element name confliction; that is, the client needs to
	 * call the method
	 * <code>{@link ReportDesignHandle#rename( DesignElementHandle )}</code>
	 * to change the element names.
	 * 
	 * @return Object the cloned design element.
	 * @throws CloneNotSupportedException
	 *             if clone is not supported.
	 * 
	 */
	final public Object clone( ) throws CloneNotSupportedException
	{
		return doClone( CopyForPastePolicy.getInstance( ) );
	}
	/**
	 * Generates a clone copy of this element. When a report element is cloned,
	 * the basic principle is just copying the property value into the clone,
	 * the other things, like container references, child list references,
	 * listener references will not be cloned; that is, the clone is isolated
	 * from the design tree until it is added into a target design tree. As for
	 * the extends reference to the parent, which is in library, the copy policy
	 * will be responsible for the specific dealing.
	 * 
	 * <p>
	 * When inserting the cloned element into the design tree, user needs to
	 * care about the element name confliction; that is, the client needs to
	 * call the method