[Zope] Clear catalog problem

[Zanotti Michele]

Hi all,
In my Zope 2.5 root folder I have a vocabulary with id Vocabulary and a
Zcatalog that uses (but doesn't contain) Vocabulary. If I use "Clear
Catalog" in advanced tab, and then "Find and Catalog" in "Find Objects" tab,
in Catalog I have the same object number I had before clear, but Vocabulary
remains empty (If I clear a zcatalog containing  vocabulary, with "find
object" I have in vocabulary the same number of words I had before clear).
Can anyone explain me this behaviour (I haven't found informations with
Google)?
Thanks
Michele