Added a bit of debugging code, so someone more knowledgeable can have a look ;)

lib/python/Products/Five/browser/__init__.py

@@ -23,15 +23,28 @@ class BrowserView(zope.publisher.browser.BrowserView):
     # BBB for code that expects BrowserView to still inherit from
     # Acquisition.Explicit.
 
+    # counter = 0
+
     def __of__(self, context):
         # Technically this isn't in line with the way Acquisition's
         # __of__ works.  With Acquisition, you get a wrapper around
         # the original object and only that wrapper's parent is the
         # new context.  Here we change the original object.
         
-        # The first segfault happens in form.tests.forms.txt in the first line
-        # of the "Widget Overrides" chapter (line 154).
-        #self.__parent__ = context  # ugh. segfault!
+        # XXX The first segfault happens in form.tests.forms.txt in the first
+        # line of the "Widget Overrides" chapter (line 154).
+
+        # What causes it is:
+        
+        # ../zope2/lib/python/Zope2/App/startup.py(199)__call__()
+        # -> log = aq_acquire(published, '__error_log__', containment=1)
+        
+        # Which causes an infinite loop :(
+        
+        # self.__parent__ = context  # ugh. segfault!
+        # self.counter = self.counter + 1
+        # if self.counter > 10:
+        #     import pdb; pdb.set_trace()
 
         return self
 
@@ -56,3 +69,4 @@ class BrowserView(zope.publisher.browser.BrowserView):
 
     def aq_inContextOf(self, *args, **kw):
         return Acquisition.aq_inContextOf(self, *args, **kw)
+