[Zope] sort

Hello again, I want to sort catalog results e.g. by title alphabetical. But when I type sort_on='title' I see the titles in order by bobobase-modification-time. What I am doing wrong ? Thanks for help Mechtild-- in der Heimat tut sich was: http://www.wolterdingen.de konteXXt - Web-Konzept-Text-Design 07705 / 919391