Bug 148747 Design become invalid when I extend a masterpage from Library
The attachment contains a report file and a library file. Reproduce: 1. Deploy the library("lib"), and open the report. 2. Drag Masterpage("page1") from "lib" to report. 3. Reopen the report, it become invalid.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/parser/ReportElementState.java
* @see org.eclipse.birt.report.model.parser.DesignParseState#getElement()
	 */
	public abstract DesignElement getElement( );
	/**
	 * Adds an element to the given slot. Records a semantic error and returns
	 * false if an error occurs. (Does not throw an exception because we don't
	 * want to terminate the parser: we want to keep parsing to find other
	 * errors.)
	 * 
	 * @param container
	 *            the container element
	 * @param slotID
	 *            the slot within the container
	 * @param content
	 *            the content element
	 * @return true if the add was successful, false if an error occurred and a
	 *         semantic error was logged
	 */
	protected boolean addToSlot( DesignElement container, int slotID,
			DesignElement content )
	{
		ElementDefn containerDefn = (ElementDefn) container.getDefn( );
		
		
		
		assert containerDefn.isContainer( );
		SlotDefn slotInfo = (SlotDefn) containerDefn.getSlot( slotID );
		assert slotInfo != null;
		assert slotInfo.canContain( content );