Protect ZCTextIndex's clear method against storing Acquisition wrappers.

doc/CHANGES.rst

@@ -20,6 +20,8 @@ Features Added
 Bugs Fixed
 ++++++++++
 
+- Protect ZCTextIndex's clear method against storing Acquisition wrappers.
+
 - LP #195761: fixed ZMI XML export / import and restored it to the UI.
 
 - MailHost should fall back to HELO when EHLO fails.

src/Products/ZCTextIndex/ZCTextIndex.py

@@ -253,7 +253,7 @@ class ZCTextIndex(Persistent, Implicit, SimpleItem):
             del self._v_lexicon
         except (AttributeError, KeyError):
             pass
-        self.index = self._index_factory(self.getLexicon())
+        self.index = self._index_factory(aq_base(self.getLexicon()))
 
     ## User Interface Methods ##