[Zope] Unexpected transation using Catalog

[Toby Dickenson]

I have a Catalog which has indexed several properties, and a form
where you can enter a property name and a property value. The catalog
is searched for objects where the named property has that value. I am
searching the Catalog using:

<dtml-let content="Catalog.searchResults({index_property:index_value})
">

Unfortunately this search is causing extra transactions to appear in
the undo log. This happens on the first search for each pair of
parameters, after starting Zope or flushing the cache. Am I doing
something wrong, or is this a bug?

Thanks,

Toby