[Zope] Searching a Catalog in Zope 2.6.1b1

I have started testing my product in Zope 2.6.1b1 and notice an odd behaviour My code looks something like this: catalog = self.ICatalog # an instance of ZCatalog called ICatalog I have results1 = catalog() print results1 # returns 25 as expected results2 = catalog({'email':'peter'}) # ...in Zope 2.5.0 print len(results2) # returns 2 as expected # ...in Zope 2.6.1b1 print len(results2) # returns 25, i.e. as if the 'email' index is ignored!!! Why this strange behaviour? A bug in Zope2.6.1b1 ? How do I go around it? I tried the mailinglist but failed to find the discussion. I also tried inspecting the code but didn't understand anything. Peter