We actually need this.

src/grokcore/site/subscriber.py

@@ -24,21 +24,22 @@
 @grokcore.component.subscribe(Site, IObjectAddedEvent)
 def addSiteHandler(site, event):
     """Add a local site manager to a Grok site object upon its creation.
-
-    Grok registers this function so that it gets called each time a
-    `grokcore.site.Site` instance is added to a container.  It creates
-    a local site manager and installs it on the newly created site.
     """
+    if event.oldParent is not None:
+        return
     sitemanager = LocalSiteManager(site)
-    # LocalSiteManager creates the 'default' folder in its __init__.
-    # It's not needed anymore in new versions of Zope 3, therefore we
-    # remove it
     del sitemanager['default']
     site.setSiteManager(sitemanager)
 
 
 @grokcore.component.subscribe(Site, IObjectRemovedEvent)
 def removeSiteHandler(site, event):
+    """Cleanup a after a site was removed.
+    """
+    if event.newParent is not None:
+        # Please note that the code for moving a site is properly implemented
+        # inside zope.site.
+        return
     local = site.getSiteManager()
     parent = _findNextSiteManager(site)
     if parent is not None: