After further investigation I found that my change to SimpleItem to sniff the response._error_format was unnecessary (although harmless) since Zope/__init__.py already does this. This check has been removed.

And since error logging was being done in SimpleItem, my previous change prevented xml-rpc exceptions from being logged.

The logging code has now been moved into the Zope/__init__ top-level exception handler to correct this problem. This also seems generally more correct since we no longer rely on SimpleItem to do-the-right-thing.