[Zope] strange error in zcatalog search results

[Yuri]

Zope Error

Zope has encountered an error while publishing this resource.

Error Type: KeyError
Error Value: 1676126652

---

    * Module Products.PageTemplates.ZRPythonExpr, line 47, in __call__
      __traceback_info__: here.fai_ricerca()
    * Module Python expression "here.fai_ricerca()", line 1, in <expression>
    * Module Shared.DC.Scripts.Bindings, line 306, in __call__
    * Module Shared.DC.Scripts.Bindings, line 343, in _bindAndExec
    * Module Products.PythonScripts.PythonScript, line 323, in _exec
    * Module None, line 8, in fai_ricerca
      *<PythonScript at /DigLib/MyApp/do_search>*
      *Line 8*
    * Module AccessControl.ZopeGuards, line 151, in next
    * Module Products.ZCatalog.Lazy, line 158, in __getitem__
    * Module Products.ZCatalog.Catalog, line 540, in getScoredResult

----

 I've textindexng2 index which search in PrincipiaSearchSource + some 
metadata.

 this error occours when I do this:

results = context.MyCatalog({'global_query': context.REQUEST['gquery']})
for result in results: <- here (line 8 above)

The catalog contains two types of objects: a container with metadata 
(derived from Folder) and a contained file (derived from File).

Other strange thing is that if I reindex some objects, the indexes 
content for that object change every time flipping from empty metadata 
and filled PrincipiaSearchSource to metadata filled and empty 
PrincipiaSearchSource.

N.B. if I search with gquery='' I get all the cataloged object correctly.

:-/