Bug 142432 MasterPage from library can't be restored to modify
Details: MasterPage from library can't be restored to modify Step: 1.New a library named lib1, and insert a masterpage named lib-mp. 2.Publish the library into resource folder. 3.New a report design and use lib1. 4.Drop the lib-mp from library explorer into outline of report design. 5.Double click lib-mp, and switch to Property editro tab. 6.Click restore. Actual result: Pop up an error message and said that the master page cannot specify size the page type is not custom.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DesignElementHandle.java
SlotHandle slotHandle = getSlot( slotId );
		if ( slotHandle == null )
			return;
		for ( int i = slotHandle.getCount( ) - 1; i >= 0; i-- )
		{
			slotHandle.dropAndClear( i );
		}
	}
	/**
	 * Removes an existing user property definition from the element. This
	 * method will remove all existing values for the property, in both this
	 * element and all its derived elements.
	 * 
	 * @param propName
	 *            the name of the user property to remove
	 * @throws UserPropertyException
	 *             If the property is not found.
	 */
	public void dropUserPropertyDefn( String propName )
			throws UserPropertyException
	{
		DesignElement element = getElement( );
		UserPropertyCommand cmd = new UserPropertyCommand( module, element );
		cmd.dropUserProperty( propName );
	}
	/**
	 * Returns a handle to the element that this element extends.
	 * 
	 * @return the parent element. Returns <code>null</code> if this element
	 *         does not have a parent, or if the extends name does not resolve