[Zope3-dev] question about bug in zope3 book. chapter 13.3

[Dan Shidlovsky]

Hello.
I got error when  try example from Zope3DevBook - Message Board :

zope.configuration.config.ConfigurationConflictsError: Conflicting 
configuration actions
For: ('protectName', <class 'book.messageboard.message.Message'>, 
'__setitem__')
File configure.zcml. In <content class = ".message.Message"> directive.

After this, I fetch interface.py from http://svn.zopr.org/book...
And find diff. In SVN (as against book)  class IMessage(Interface) has no method
__setitem__. Line 13 and 14 in interfaces.py 

Now, without this lines all work OK. Why?
Thanks.

PS. It can be necessary to add bug in Collector?